In addition to picking up some knitting tricks, I've become way better at doing laundry. In the past, I would never hand launder anything, and rarely buy anything that required hand laundering. While still not a fan, I now have a much better idea of what tags that say "hand wash only" mean it.
For instance, if a sweater is more than half acrylic, it probably will not shrink in the washer on cold. In fact, anything not 100% wool will probably come out fine if you stick it in a mesh zipper bag (to avoid weird sleeve stretching), on cold, and don't put it in the dryer.
A brief foray into fibers as well as felting (fulling, to be more exact) techniques will teach you what treasured sweaters will be unilaterally destroyed. It will also teach you to swear by superwash yarn when giving gifts that you don't want to see subsequently destroyed.