Defense is expensive and probably not worth it in leagues with a salary cap.

Defense is important but also costs money. It's worth paying for good fielding at the positions that make a lot of errors (SS, 2B, 3B). get a Catcher with good arm unless you're in a theme league where you don't expect much running, arm is expensive but worth it if a lot of people play speed teams.. Range is probably overpriced but be careful about D- range players some of them are awful. CF is busier than than corners so some people pay for glove here.

In general, I think most owners underestimate the importance of defense, especially behind stud pitchers.  I think it is probably worth it to pay for good (tho not great) defense.  Also, IMHO it is probably worth it to pay for fielding or range, just not both.

While some owners value range more than others, my thinking on it is simple and straightforward, especially for open leagues.  Provided you've drafted a good team, you can win a lot of games with a SS/2B combo with  A/D-  fielding and range ratings (.980 or above fielding and RRF of at least 4.50), and a catcher with an A+ arm. I'm ok with a D/D- guy at any other position except CF. But just as rbow923 advised, you have to be careful with the D/D- guys because they're not all created equal, and some of them are absolutel butchers in the field.