I've actually found it to be extremely useful part of my daily routine and when I need to break the routine for whatever reason (I live nomadically so my routines are always changing), my whole day is usually a lot more uncomfortable (i.e., my digestive system and bowls feel slower).
I still haven't identified how all this works, but it's an interesting anecdote.
Coffee acts as a laxative. Interestingly, this effect is observed in decaf as well.
Source: Boekema PJ, Samsom M, et al. Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol Suppl. 1999;230:35-9. PMID 10499460