Medically you are advised to wait a year to 18 months between babies. That's because pregnancy, (and I am sure anyone who has been heavily pregnant agrees) puts huge demands and strains on your body. The reason why we are supposed to take vits during pregnancy is because the growing foetus consumes all our intake and most of our stores. Which means should you decide to have another baby within a few months of your first, you run the risk of having a smaller birth weight baby or the baby coming early. They say it takes 9 months for your body to get where it is at birth and it will take at least 9 months for your body to get back to where it was before. Its important to let your body rest so that its in good shape for your next.
Saying that people get pregnant straight after their first and everything is fine.
Personally, I like to spend time with my babies, drink in their smiles and cuddles, watch them develop and devote my time to them for at least a couple of years, which I don't think I could do if I had a similar pregnancy as I have with my first two, and then a newborn to care for... They'd get kinda pushed out.
Having an 8 year age gap has had many benefits but it means that my girls won't really play together, more the older one entertains the younger one while I'm cleaning or making food. But saying that I got to bond better and could easily breast feed because the eldest could entertain herself.
Don't get me wrong, I'd love another right now, but I know that my body needs some down time, especially as I am still breastfeeding. My friend had a toddler and a baby and she had lots of trouble bfing because the toddler was so demanding.... and I want to be able to give my next one the best start I can.