Some people believe it increases indurance, coffee is not the best way of obtaining endurance increasing caffeine though - I think carbonated drinks are better. The effects differ from person to person, personally I don't think it helps me.
caffeine will increase your FFA(fats used for endurance exercise) and thereby spare your muscle/liver glycogen;ideally taken one hour pre exercise,but there are so many individual responses to it best tried in training first;consistently shown to increase time to exhaustion ie you run further/quicker!
I always have a strong cup of tea an hour before playing football - with some sugar. I find it helps me up to keep going longer - and get off quicker. But I think so much of this kind of ritual is psychosematic (spelling?!).
As many of us know, the biggest challenge to running is the mental one. If you think something will help, it normally does.
I avoid caffeine before a race because of its diuretic effect and when I analyse my performance if I have taken a caffeine tablet (such as proplus) it usually has little or no effect so I put the perceived improvement down to the placebo effect.