[manigandham]

This always comes up but people seem to just ignore the complexity: What exactly is supposed to happen when the spend hits your budget?

Even a few bytes sitting on S3 continue to incur charges and it's hard to be real-time with spend tracking at the scale of these providers so the only option they have is to delete your entire account immediately. Is that what you want? Who would?

For most companies, business continuity matters. The proper solution is to use the budget and reporting features to check your work.