Well,
I built my place in 1988 when I was 20. My parents let my brother and I close in their garage. They said," If you pay for it, you can do whatever you want out there." We built several layers of walls until they were 12" Thick. That allowed me to basically play drums anytime I wanted. I had a little 8-track reel-to-reel studio (a Kelsey 24x4 mixer modified to be  a pair of 12x4's in the same frame, with a Fostex A4. Whew- I thought I was bigtime when I got that set up!)
It was great to have. My friends and I spent untold hours playing out there.
Locally, studio time is expensive, and any place to rent to practice is roughly $500 a month. If you are willing to be locked into paying $250 a month for a long time, you can build quite a decent studio.
Or spend 5 hours a month in a commercial studio.
So, for me - it served 2 purposes.
I have yet to actually "release" anything. I can never seem to get the bands past the garage stage. I have a hard time finding musicians who don't drink like fish, or think Pot is one of the "5 basic food groups".
But I have recorded several 7" singles for others that have been released (One of them sold 3,000 copies the first week!)
And I've recorded a Jazz CD for my brothers band, that is sitting on the shelf...I'm still not sure why they canned it. I know the label owner and my brother had some words at one point, and that's my guess.
Anyway, I did it because I liked being able to have my own place to work on stuff, and to be able to tinked and play around with sound.
I had worked in several diferent construction trades, so actually building it didn't take very long. My whole band was made up of carpenters, and sheetrock/painters, so once we had all the supplies delivered - we would work on it at night. We set the walls in one weekend, ran electric in one night, insulation and sheetrock took two more nights, and then it was just a matter of mudding the sheetrock, sanding, and then priming, painting, and we hung carpet tiles on the walls (18"x24" doormats made form carpet.... you know, those samples that the carpet places have.)
It looks cool, and the sound is great.
But sadly,  I had to give it up because we took in a friend who has lupus and her family wouldn't help her. 
So it came down to - do I let her wind up homeless, or do I keep playing drums?
So to make room for her, my brother moved into the studio, and she moved into his room.
Obviously, my conscience (no matter what anyone thinks of me) wouldn't allow me to let my friend die as a homeless person on the street - even when her own family would.
So, I gave up the studio. At times it's been hard because it set me back musically, but I'm working on a new gameplan that is going to allow me to purchase my own place, and build a studio there.
And this one is goingto be bigger, and better - and actually have a bathroom and kitchenette in it! No more traipsing through the house to go to the bathroom, or to make some coffee. 
 
 
Tim