As far as I'm concerned, the big difference is that nobody paid to see you play in the garage. Having knobs fall off, strap pins rip out, bridges falling appart, necks warping, electronics short out, jacks fall off or going way out of tune just isn't acceptable when people have actually paid money to see you play. If this happens in the garage... yeah, inconvenient. If it happens on stage in front of a paying audience, you're going to look foolish. Not to mention the fact that a "working" bass is going to be moved around between back rooms, vans, stages etc, where it's going to probably get knocked around a bit. It better be able to take it.
That said, most budget insruments these days are pretty "gig worthy" in my opinion. Back in the days when budget instruments meant plywood and really bad electronics and sub par wiring jobs, this was much more of an issue than it is today.