Another benefit of not having children is that you won't have to worry about losing friends due to having children. Though this might not be the case for many women, there is still that slight chance.
In fact, many articles I've read give that as a cost to having children. It's understandable, considering most of the time after childbirth is spent taking care of the child and spending time with a significant other, if there is one. Married couples with children tend to be focused on their children and work. This doesn't leave a lot of social time, so friendships might suffer. One article from Canadian Family explains how one mom lost her best friend due to not having any time for a social life with three kids. One kid allowed some freedom, but she says her friendship went downhill after that, and now she really only has mothers as friends. An article in Cosmopolitan says the same thing about friendships taking a blow when one friend has a baby and the other doesn't.
Though there are many benefits of not having children, there are costs as well. One obvious cost is that if all women decided to not have children, there would eventually be no younger people left and, eventually, no people. This would take quite a while, but you get the point. There needs to be enough women reproducing to make up for the deaths, but anything more isn't truly necessary. In a couple blogs on The New York Times' Web site that related to the recent climate talks, there is mention of the problem of overpopulation at the global level, not underpopulation, so it seems there is no need to worry.
Costs of not having children can be plentiful as well, though I am only giving two in this article. The other personal cost that I have seen is that if a woman decides not to have children, it may be much harder to find a man who shares the same view. Though not all women want or need relationships, many women end up being in relationships. At a certain age when a woman is with someone she intends to marry, the subject of children will eventually come up. If the significant other demands children, but the woman doesn't want any, that is a major difficulty in any relationship.