I've bought quilt kits for some of the same reasons that others have mentioned.... not so great at putting color together and it's a timesaver when I don't have to run all over to get the colors that I want.
My first attempts at putting together color combinations have left me less than thrilled with the final quilt. I match things too much and don't have the contrast to make the quilt "sing." So someone else's expertise helps me with color choices.
Also, I live an hour away from a quilt shop and am currently staying with my elderly mother so my time is limited for making shopping trips. It helps me bunches to have everything I need so that I don't have to wait until I can make a trip to the nearest LQS. So quilt kits bought on sale or at ebay have been a real find for me.
Can't believe the deals that some of you have found at thrift shops and estate sales. My best deals have been old quilts that I want to replicate one day...they're cheap but pretty worn.