"The problem, it turns out, is that your average computer motherboard - unlike a hobby PCB - is actually a multi-layer affair. If you don't get every single solder joint absolutely perfect, the solder fails to connect one of more of the sandwiched layers and the system simply won't work."
When I first started working on PCs, I replaced capacitors all the time on motherboards and other cards. My favorite solder job was an Intel 90Mhz Overdrive processor that had been dropped (not by me.) After straightening out all the pins, two had broken off, and the boss said to throw it away. I took it home and soldered pieces of a paper clip in place of the missing pins. That system ran without any issues for two years.
I was only making $8.00 an hour, and all my systems were built out of the trash as I couldn't afford parts at the time. That Overdrive chip cost $400.00 back then. I didn't have money, but I had time, so I built bad ass systems out of the trash. Time, solder, and ingenuity built me systems for free that would have cost many thousands of dollars if I had to buy parts instead of re-build.
Biting the hand that feeds IT
