There are a great number of attractions to Lego. Some people buy sets for their kids, some for the minifigures and some just because they want the parts. Additionally, some people are selective about which sets they buy because they either can't afford to buy all the ones they want or are trying to hold back on buying Lego.
Personally I buy sets for the particular vehicle or building portrayed in the set. Occasionally I buy a set for a specific minifig but only cheaper sets.
What I'd like to know is; what are the things that factor into your decision to buy each set?