If you like freewheeling and just coming up with Whatever by chance/guess each time you make an exposure, then you don't need one.
If you want to print without a timer and get the best repeatability, you might want to stop down so you can use longer exposure times. That way small variations in time don't have as large an effect on the print.
You really don't need one with lith printing. Small exposure variations don't really matter, and the times are so long that you can just use a clock.
But enlarger timers are so ridiculously cheap on the used market that I would just pick one up. You should be able to get a Gra-Lab for next to nothing. They are a hassle, as they are not repeating timers. But they are cheap and get the job done.