It all depends on where you're starting point is at. A decent cook, who plans well and has spent some time on the forum asking or reading can gain a ton of insight to assist them in cranking out a decent performance.
I don't think classes are necessary to win at all, as many here have proven over time, but a comp class will help with some of the finer points, provide creative ideas to adapt to your own style etc and many do have a lot of fun hanging with other cooks as well.
Good Luck !!
Lonestar 24" Vertical offset w/ Insulated Firebox & Performer Platinum
Former owner: Jambo Backyard, Klose BYC, Med. Spicewine, Pitts & Spitts, XL & (2) Med. BGE's, 22" WSM & (2) 18" WSM's, 18" & 22" Weber Kettles