I can only speak for my own experience, but it has saved my wallet a couple of times in the past few years. The spending limit is advertised fairly explicitly just that: a customizable limit on your monthly spending [1]. If it doesn't work as intended and you end up with a bill larger than the limit you set up, you'd have a rock-solid case for disputing the extra charge.

[1] https://azure.microsoft.com/en-us/pricing/spending-limits/