If your node remains online then you're contributing your channel funds to help route other people's transactions. The more channels you have open the more routing you can do also.

If you're not keeping your node onoine then you're going to have to start it at least as often as the timelock runs out for the channel (you can verify this number from its stats). If you don't put your channel back online before this time is up, there's a chance the other party can claim your funds afaik.