It’s your choice. You could receive a fedimint payment to your own federation, to your Lightning node, or you could swap from Lightning to base chain.

Why keep it in a fedimint?

You don’t have to manage a Lightning node.

You get more privacy than just using Lightning.

If you’re nontechnical, then a federation of trusted people can manage your keys for you (and potentially restore your access if you “forget your password”).

Like lightning, it will likely also be cheaper to use a fedimint than to transact on the base chain.