I started on C25k in the autumn and have worked my way up to a handy 25' circuit. The "official" advice is now to extend my runs further - but actually this is a nice loop on fairly even ground, off-road, which is in short supply in my hilly area. And as I have to take time out of my working day at this time of year to run (or its dark) I don't want to be out any longer really.
So I am aiming to stick to the same route but hopefully get faster, but what will I miss out on by not going further? I am no spring chicken (well into my 50s) and 3xweek seems to suit me well. Running to keep on top of weight (it works for me!) and for general fitness.