When I was in jr high and high school, everyone wanted me to work on their rides. It got to be over whelming and I was giving away my time and parts. In retrospect, it was foolish to wear my heart on my sleeve. I started charging for parts and labor. I was a teenager, I couldn't give parts away. If I wasn't paid, I took my parts back.
Today, I only work on bikes for very close friends or family. I did spend several days trying to rebuild my now-ex girlfriend's old bike. A curb find 1990's Huffy that should have been scrapped. New bearings, rear brake cables, new seat, new grips, new pedals, and a lot of time in labor. Wasted.
I fixed up a 1979 AMF 3-speed, a pretty purple and white cruiser for my mother. She never rides it. I rebuilt my step-dad's 1978 Concord New Yorker with a 1979 Columbia parts bike. I invested little money in it, but a lot of time and presented it for father's day. We don't always see eye-to-eye, but we ARE family and he was so thrilled to see it rebuilt. New bars, stem, back wheel (transmission was good, but rim was smashed), all new cables, grips, and tires were swapped. All from that Columbia. He has ridden it on occasion.
I rebuilt an old Free Spirit for my dad a few years ago. It got him back in biking, and when the derailleur gave out on a 20 mile ride, that was it. He bought a new Giant!
I barely have time for my own stuff, and since I quit doing favors for everybody my life has been simpler. I send people to the LBS in town; they scratch my bike and I scratch theirs!!