No one has said that GFI's are very sensitive to subtle things...
Now for some redundant comments:
So sure, you can plug into a straight 30 A plug and do all sorts of things with no problem.
But if there's one little electicity leak (i.e. ground fault)- the GFI does it's job.
While I can say they are "sometimes overly sensitive", the other answer is yeah, the human body is "sometimes overly sensitive" to a ground faults too- so we don't want to dismiss the issue.
A regular breaker protects against overloads and over heats.
The GFI protects against subtle leakages (and typically overloads too).