I became a home mechanic for simple economic reasons. I have 7 kids and all have had at least one bike and or raced at one time or another between road, BMX and MTB. We have had as many as 16 bikes in the stable. If I had to pay a professional for every bit of work from simple adjustments to major tune ups and crash damage repairs, I would have been out a bunch of cash. I was doing most work myself when I started to run into some wheel problems 6 or 7 years ago. My LBS did quick repairs and truing but never properly tensioned the wheel or in retrospect recommended a rebuild. Frustrated with continually paying others to do this "black magic", I decided to learn and have never looked back. The three bikes I ride are all on wheels I built. I build and tune wheels for friends and relatives as well.
Today, the only thing I would need from my LBS from a mechanical standpoint is facing of head tube or BB. I still buy some parts and accessories from a few LBS's to keep decent relationships and keep some money local.
I would say the greatest satisfaction for me in tapping "The Mechanic within" is that barring complete catastrophe, I can make it home on any ride. My road rides are routinely 35 - 70 miles whether on my single our our tandem so this is important. I'm more of a preventative maint. kind of guy so stops are pretty much unheard of but the knowledge that I can do anything I am call to do is very satisfying. I regularly stop to help others and that is pretty satisfying as well.