You will get a lot of varied answers on the usefulness of MagicBands and it is ultimately subjective. Many people don't find them worthwhile at
Disneyland.
Personally, I find them to be amazing at Disneyland. As the person who manages everything for everyone and plans the entire trip, it makes it much easier for me. I book park reservations and associate a MagicBand to a ticket, and I book all Lightning Lanes. Instead of having to pull my phone out constantly, each person can scan their band for entry into the parks and to get onto Lightning Lane attractions. Part of our group can ride something with Lightning Lane and I don't need to go with them.
MagicBands are not necessary, and they are pretty expensive, but they can also be re-used on each trip and used at Disney World. I find it to be worthwhile and it makes my experience at Disneyland better, easier, and less stressful. You also don't need to charge them for just scanning into the parks and lightning lane.