Committees are repositories of policy expertise. Committees are policy incubators. Committees possess disproportionate control over the agenda in their policy domains. Committees are deferred to, and that deference is reciprocated. This means that, instead of sorting out the facts for each issue or bill that comes up for a vote, members of Congress are willing to defer to a committee and grant its members leeway to make important decisions regarding legislation in their areas of expertise.
Committees can do things to discourage opposition to their actions.
They can induce cooperation not only by threatening to oppose dissenters' legislation after a bill is voted down, but also by threatening to attach unpopular riders to a bill before it reaches the floor. One important example of this was the decision by legislators from the South to attach busing requirements to the school integration proposals that were intended to support the Supreme Court's ruling in Brown v. Board of Education. This action ensured that, although the bills enjoyed strong bipartisan support, they were not enacted because of opposition to the busing provisions. Committees also have another mechanism through which they can kill legislation that has already been enacted. Many bills frequently exist in different versions in the House and the Senate.