Most of the time, buses operate to time or few minutes late. Thats in my experience anyway. Paper timetables can be used to plan trips, or to see if its worth using a particular route for a regular commute. Realtime electronic information is then useful on the actual day you're travelling, to check its all running ok. Paper timetables and electronic realtime information should work hand in hand. In the same way I like to see which particular scheduled train I am planning to get, then use Realtime Trains and the passenger displays at stations to check its still running to time.
Well I don't know your experience, but in my part of the world it is not unusual for low frequency buses to way beyond a few minutes late. Delays of 10 or 20 minutes for hourly services are not uncommon especially during rush hours. Indeed so bad have the delays become, operators have been making timetable changes several times a year to try to makes them able to stick to schedules. And some higher frequency services have been advertised as "Approximately every XX minutes" at times so no exact public timetable exists.
Published timetables can be stored electronically and updated quickly & easily as required, and when accessed via a website or mobile app can allow operators or PTEs the ability to easily alert passengers to timetable changes. This is why WY Metro are moving to digital by default. There should always still be the option of requesting a printed version on demand, but printing thousands only for them to be thrown away is a waste nowadays.