How often do you refresh your sandbox(es), if you have them?

it depends on your need, note that there is a limitation for sandbox refresh count

NS

typically

provisions as if you will refresh around once a month typically - however, I find my cadence varies drastically depending on if I'm in an active long term project.

monthly, if possible.

We have one sandbox I refresh monthly on 15th. Our other sandboxes are trickier to refresh due to linked integrations so they are way overdue for a refresh

Our Stage sandbox has also active integrations towards other dev environments. We refresh it about a month before the upgrade to be able to request an early upgrade on it so that we can test the integrations before the upgrade. Our Dev-sandbox (should) be refreshed every other month but there's always some active development going on that makes us postpone it.

I've become more aggressive about refreshing (especially 'dev' sandboxes) since the rise of SDF. Unless it's something SDF can't do, I expect to be able to easily recreate any in-flight development via SDF deploy (provided of course that SDF supports whatever it is we're doing)