Subst. slow blow w fast blow fuse:normal practice?

A tech guy at Krell told me that i can always substitute a slow blow fuse with a fast blow fuse double the value (example:0,8A slow blow fuse with 1,5A fast blow fuse)Is it a normal practice?I would greatly appreciate your enlightment!
Although I would not recommend it, doubling the fuse value would probably be enough to deal with the inrush current at turnon that is the reason for the Slow Blow type. And, for most kinds of faults that will blow the fuse, doubling the value won't matter either. The kind of fault which blows a fuse is a short circuit, and the current draw may be upwards of 10 amps, so the difference between 0.8 and 1.5 is insignificant. Note that I said MOST kinds of faults. Some faults might slowly cook your amp at 1.4 amps.
In a pinch, a 2X fuse is better than a jumper! But, if you have just had a fuse blow it is not the time to experiment.