I also think it'd be good for companies. If you usually pay (say, numbers don't matter, except that AWS or whoever doesn't care until they get bigger I suppose) 1k-3k and set a 'don't surprise me too much' limit of 5k, then when something unexpected happens, instead of having a bad time pleading with them to let you off 12k or whatever and feeling cautious about using it again perhaps with some sour taste even if they do let you off, you think 'woah, glad I have the limit', and pretty much get on with your day; AWS or whoever gets an unexpected 2-4k instead of writing off 9-11k, and keeps the happy customer (at the customer's expense instead of its own).