I wanted to pay off my SLs above 5% interest rate and save up a down payment on a house and finish nursing school. We did that, and I'm glad we didn't wait any longer than we have. We're struggling with infertility (in spite of starting trying at 27) and doing our first IVF cycle right now. Thanks to frugality and the options money buys, we have this option, even though it's $17,000 out of pocket for each cycle. (Very very few people have infertility benefits, even diagnostic).
Anywhoo, I advocate for getting your ducks in a row but not waiting too long, because you never know what life will throw at you.
ETA: oh duh, and a stable partnership. For me that meant marriage, but I like tidy paperwork and taxes =)