It can be a liability in a few ways -- the hobby can take time away from friends and family, there's a risk of flooding the house, and it can be tough to go away on vacation. It can also be hard on the bank account.
But it's an asset in so many more -- reefs can be an educational tool for children, help people relax, make you feel closer to nature, add beauty to a home/office/school, and having a hobby keeps the mind sharp and provides endless entertainment. Reef clubs are places to meet people, pass on knowledge, trade stock and learn new things. Forums are another social aspect of the hobby -- people make friends online that they'd never meet if they didn't share a similar interest; sometimes the friendships are with people on the other side of the world, and many people who meet here get together in person at events or club meetings. Having a reef has taught me about the ocean, made me appreciate nature more, and the joy I get out of the hobby is immeasurable.