A number of commenters (at least one here and several elsewhere) have asked why we need a debt ceiling. If the Congress wants to spend less, why don’t they just go ahead and spend less?
The answer is that different spending programs command different majorities. Snip and Snap vote to fund rabbit hospitals; Snap and Snurr vote to fund trapeze subsidies; Snurr and Snip vote to fund lava lamp research. Plausibly, they’d all prefer to eliminate all these programs. Even if Snap thinks rabbit hospitals and trapeze subsidies are both great bargains, he might not be so happy about getting two for the price of three.