"In Islam, iddah or iddat (Arabic: العدة‎‎; period of waiting) is the period a woman must observe after the death of her spouse or after a divorce, during which she may not marry another man.[1] Its purpose is to ensure that the male parent of any offspring produced after the cessation of a nikah (marriage) would be known. The length of iddah varies according to a number of circumstances.

The iddah of a woman divorced by her husband is three monthly periods,[2] unless she is pregnant in which case the ‘iddah lasts until she gives birth,[3] or unless the marriage was not consummated in which case there is no `iddah,[4] or unless she does not menstruate, in which case "the scholars say that she should observe an ‘iddah of a full year, nine months for pregnancy and three months for ‘iddah."[3]

For a woman whose husband has died, the `iddah is four lunar months and ten days after the death of their husbands,[2][5] whether or not the marriage was consummated.[4][6] The period, four months and ten days after the death of a spouse, is calculated on the number of menses that a woman has."  (Source)

And again, Allah Almighty Said:

"(Remember), if you are in doubt about the ‘iddat.’ of your women, _ either because they are past the age, or haven’t yet started to menstruate _ it lasts three months. The ‘iddat’ for the pregnant women (is three months, or it) lasts till the termination of pregnancy. (iddat: the period after divorce during which a woman is forbidden to remarry). Allah (grants a leeway and) makes matters easy for the one who fears Him.  (The Noble Quran, 65:4)"

  

From www.answering-christianity.com/muta_forbidden_with_shias.htm:

  

1-  Careless divorce will bring sin upon you:

Muta marriage was a temporary marriage that destined for divorce, which Prophet Muhammad, peace be upon him, is said to have allowed for Muslim men who fought in battles in distant lands.  They were allowed to marry women there temporarily.  Allah Almighty has thoroughly prohibited all forms of temporary marriages, and has stressed the holiness of permanent marriage in the Glorious Quran.

Was it legalized prostitution?  Was it a form of pimping women and men for just sex?  Absolutely not, because even with the Muta marriage, there was still the requirement of at least two witnesses testifying that the couple have married (announcing the marriage publically protects everyone.  Ex: Married women are not approached by other men as single women, and pregnant women are known to be pregnant wives, not pregnant harlots), the dowry payment upon the husband, and Muslim women still had to go through the Idda period after the divorce.  So it was a legitimate full marriage but with the exception that it was destined for planned divorce (i.e., termination).  Allah Almighty ultimately forbade intentional non-permanent marriages. 

Here is what Allah Almighty Said regarding divorce in the Noble Quran.  It almost always brings sin upon the regular married folks.  However, if a man is engaged with a woman, and they had a marriage contract already done, with dowry payment, witnesses and announcing to all people in their community that they got married, but they have not yet consummated the marriage through sexual intercourse, then there is no sin upon them if they divorce, as long as they have not consummated the marriage:

‏2:236 لاجناح عليكم ان طلقتم النساء مالم تمسوهن او تفرضوا لهن فريضة ومتعوهن على الموسع قدره وعلى المقتر قدره متاعا بالمعروف حقا على المحسنين

"You bear no sin if you divorce your wives AS LONG AS YOU HAVE NOT (ma-lam مالم) had (a sexual) contact (with them), and before settling (the amount of) the nuptial premium (for them). Yet, you should make provisions for them (even then); the affluent in keeping with his means, and the poor according to what he can afford. A fair provision is an obligation upon the pious.  (The Noble Quran, 2:236)"

  

Ma-lam مالم in Arabic means "as long as you have not," which makes it a condition and a Law.  The meaning of the word مالم as "as long as you have not" is very well-known in Arabic and the translation is also proven by ample English translations of this Noble Verse.  So irresponsible divorce after the consummation of marriage (after sex) will bring sin upon the irresponsible and guilty one(s).  The Noble Verse is crystal-clear about this.

  

2-  The solemn holiness of marriage (ميثاقا غليظا):

Also, the covenant of marriage in the Glorious Quran Is a Mighty and Solemn Covenant ميثاقا غليظا (mee-thaa-qan gha-leetha).  This exact phrase is mentioned three times (4:21, 4:154, 33:7) in the Glorious Quran for the following Covenants:

1-  For the solemn covenant of marriage between the husband and wife.
 2-  For the solemn covenant between GOD Almighty and the Prophets.
 3-  For the solemn covenant between GOD Almighty and the Jews on the holiness of the Sabbath.

Again, please see Noble Verses 4:21, 4:154, 33:7.  Divorce is allowed, but it is a detested lawful thing to Allah Almighty.  Abusing it or misusing it will bring sin upon you.

  

3-  One wife is the most preferred to Allah Almighty:

Furthermore, Allah Almighty made it crystal clear that He best prefers for Muslim men to only marry one wife, each.  Messing around with marrying multiple women is a slippery slope that could bring sin upon you:

Noble Verse 4:3 "If ye fear that ye shall not be able to deal justly with the orphans, marry women of your choice, Two or three or four; but if ye fear that ye shall not be able to deal justly (with them), then only one, or (a captive) that your right hands possess, that will be more suitable, to prevent you from doing injustice."

Marry one woman to prevent you from doing injustice.  This is further supported also in the following Noble Verse:

Noble Verse 4:129 "Ye are never able to be fair and just as between women, even if it is your ardent desire: But turn not away (from a woman) altogether, so as to leave her (as it were) hanging (in the air). If ye come to a friendly understanding, and practise self-restraint, God is Oft-forgiving, Most Merciful."

Polygamy is allowed by Allah Almighty, but like divorce, it too is a detested lawful thing to Allah Almighty.  And most certainly, abusing it or misusing it will bring sin upon you.