I suppose when you're starting to get play on the crank for cartridge bearing BBs. Things like squeaking if caused by the BB is usually due to incorrectly torqued BB cups or did not grease the threads. But too often squeaks are caused by something else other than the BB even if it seems the noises are coming from the BB.
Other than problems, cartridge BB's can last a very long time. Over 10,000 miles at least even for low end cheap BBs.
BB's should be serviced once a year. Even if they are sealed bearings the cranks should be removed and everything cleaned and open bearings cleaned and greased. With modern 10,11,12 and 13 speeds you will generally have problems with the derailleur adjustment and have to have work done on them more often than that. I think that reliable manual shifting went out the door after 9 speeds. Now the outstanding feature of electronic shifting is reliable and accurate shifting but I just have a poor view of plugging my bicycle into an electric outlet.