Congress passes a bill to authorize a government program and expenditure of funds before passing an appropriations bill to approve the expenditure of funds. Authorization bills cover multiple years (such as 3 or 6) whereas appropriations are usually annual. Some programs such as so-called entitlements do not follow this process.
One advantage of periodic authorizations is that they allow Congress to make changes to programs. While they can always do so, the difficulty in passing legislation makes it unlikely to happen unless a bill must be passed because an authorization is about to expire. I wrote about a similar situation with the difficulty of repealing legislation here.
I suggest a Constitutional amendment to require authorization bills at least every 12 years. This would ensure that Congress revisits every program at least that often. Without this requirement it is difficult to end programs that no longer are needed; they continue because the process of repealing them is too difficult. But if an authorization expires, there is nothing for Congress to do but to let it expire.