Due to the fact that you must claim everything you make during the entire year, and I do side work in my garage, I am legally obligated to claim it and it ends up being to my benifit every year. I only make a small amount but since I can claim part of my tools and part of my property (actually part of the garage) the write off ends up being more than I made and my tax return is higher by doing the right thing. Every time I go to get parts for someone elses car I write down the mileage, a certain percentage of my utilities etc are all write offs. I could probably push it legally alot farther than I do but since I use the tools and garage on my own cars I don't claim the max I could. Kinda funny how many people lie to the IRS and pay more than they would if they didn't.
edit:I do my own taxes using Tax Cut Pro adn have them looked over by a CPA and he laughs every year when I show him. Alot of places don't want to touch home bussiness/ self employed (H&R Block)