It’s not a formality. Continuing Resolutions (CR’s) and especially shutdowns can really affect people’s lives and society at large. People who require critical resources might wind up going without.
It also winds up costing the government more overall to go through this every year.
This appears to have decent information on why shutdowns are bad:
https://www.crfb.org/papers/government-shutdowns-qa-everything-you-should-know