It's fine to say something like "the bible is all we need", we have the bible, so we don't need prophesy. That's probably true, but look at them, look at the churches that don't live by prophecy. Decisions are made by majority vote of councils, using man's knowledge and wisdom. Many are in debt, and are forced to ask for donations on the street like beggars or conduct raffles or other fund raising events. Sunday schools close, youth groups close. How many of them actually consult God's will on a matter. Should they really have closed the Sunday school because they couldn't afford it, or perhaps it was God's will to keep the Sunday school going, but rather cut costs in other ways, like turning off the unnecessary airconditioning or something. Some get the wrong pastor, and he or she ends up leading them astray. Or they are so set in their ways that the church is the same now as it was 20 years ago. Same programs, same routine, same results. If only they had consulted God's will there situation might be very different. Where are the churches praying and fasting and drawing straws? The lack of personal direction and prophesy in churches opens the way for people like Rick Warren and his purpose driven church to gain foothold.
It's fine to say "see what the bible says", but that doesn't cover every situation, and it is still very much open to personal interpretation. For example, should the church take out a loan from a bank?, should it move to another building?, should it hire this youth pastor or another youth pastor. The bible can't answer those questions usually. Sometimes specific direction from God is required and this can come via prophecy. Whether a known prophet in the congregation or if God reveals the answer to the pastor himself, perhaps the pastor is a prophet or functions in prophecy himself.