So most of my experience is with cup and cone bearing, which are pretty easy to maintain. With newer, cartridge bearings I haven’t been paying much attention to it. Have just been riding until there’s a problem. Assuming that as long as there’s no issues, it’s fine.
Curious how often people are doing any kind of maintenance for the more modern, sealed/cartridge style bearings for wheel hubs, headsets and bottom brackets. And are you trying to clean and repack them with grease, or just replace as needed?
I generally try not to ride in the rain and I don’t power wash my bike so my sealed bearings seem to last virtually forever. The only ones I maintain is my Campagnolo bottom bracket - cleaned with fresh grease once every couple of years (these are serviceable ceramic bearings).