I had one bike that ate a cartridge bottom bracket in less than a year. That taught me about the importance of drain holes.

Clean and repack according to conditions. A lot of wet and sand, do 'em annually or more. Sunny days only, every five years or when they complain.

The trick is, if you wait to long the bearing race will be damaged and will need replaced. Too soon and you waste a dab of grease and some time.