Well, they don't necessarily look at all departments and all programs. Sometimes a department will be passed over without questioning, because there's nothing there the committee wishes to examine. That's pretty rare.
Most departments get a run, but the committees sometimes feel that they don't have enough time to deal with particular things. They report that to the Senate. Basically, that's taken up at the next round of estimates hearings. At the supplementary hearings or the additional estimates hearings, they're taken up again. But the committees have no power to approve or not approve the estimates. They simply report to the Senate on matters they're interested in. It's up to the Senate to actually pass the appropriation bills.