To me its mostly a time issue... the faster I work on a car and get it done the more I get paid in theory... I would much rather solder but where I am most people don't want to pay (poor economy). We were trying to do the whole solder of a harness into the car that way when the customer is done with the unit when we pull it out we just pull the brain and leave all harnesses and bypasses in... and have them buy new ones but my boss wasn't for it... We use butt connectors for all appropriate connections if its vats wiring in a gm car or something really small i'll use solder... I use solder in my own vehicle with glue heatshrink. Certain harness i'll use solder with to hold resistors/diodes better.

I also agree solder may be more reliable in the LONG run. but we've had installers using butt connectors and t-taps for 8+ years and no problems yet... I KNOW Y'ALL GONNA HATE ME FOR THAT!! Its not me, its my job... SORRY!!!