Hi Guest,
If you have your bitch spayed before her first heat, there are proven health benefits of reduced cancer. If she is spayed before her second heat, the benefits are reduced by about 30 percent. It seems that anytime after that, does help out over all, but will not guarantee anything.
Here are some websites that might help you decide if you want to have her altered.
Purina's view quick rundown of benefits links and more information There are those who believe spaying is uneccessary unless there is a health problem. Others believe that a matured female is best. That's ok. It's pretty much an individual choice on the part of the owner.
I just know from my own experience that dealing with heat cycles is harder than I thought it would be. I didn't want to worry about unplanned pregnancies or pyrometra. I also didn't like my dogs personalities changing so much with their version of PMS and "Must procreate now!". :)
I've had spayed females for years. To me, they make the best pets. Loyal, watchful, and focused on my family.... not on twice yearly breeding urges that they have no control over. Both Samma and Chienne were spayed before their first heat cycle. No problems ever came out of it. But that's my experience and preference ;)
I hope this helps gives you enough information so that you can make your own choice to determine what is best for you and your bitch.
good luck,
toodles