1. They're handy for showing your appreciation and getting past a common "I don't _want your money_" barrier in my region.
If I pass out a bunch of silver rounds to friends with krakens on them while loudly proclaiming "8 ARMED SEA GODS, TO COMMEMORATE THE FACT THAT MANY HANDS MAKE LIGHT WORK" everyone who helped me smiles broadly, laughs and receives them. An aura of gratuity emanates from the situation from everyone involved.
If I were to pass out envelopes with a 20$ bill in each, it would make everyone feel weird. Many would get returned, I probably wouldn't have friends anymore.
2. Garage sales ran by older people. I've found a silver coin has, on average, a higher buying power than equivalent cash. For 1oz of silver, a nice gentleman agreed to trade a circular saw, bench grinder parts, an electric motor, lathe parts, a few hammers, a tool box and an angle grinder last year.
3. Gifts for kids. 1 oz silver rounds are not that expensive, shinier than most objects, larger than most people expect, and tend to be received with wide eyed awe every time I've given them as gifts.
Silver is fun.