A given wire gauge can only carry a limited number of amperes. When that limit is exceeded, the wire dissipates power as heat, sometimes enough to melt and burn.
A few weeks ago I was wiring a Nokia hands free kit on my brother's Renault.
Took the center console off and found the cigarette lighter wiring. As the hands free kit had 0,50mm wiring, having the full 20 A from the lighter circuit on that wire would be a fire hazard, should it short circuit. So, I used some wire the same size as the one on the lighter to take power to a free fuse holder with a 3 A fuse, from then on I used the thin wire.
In short, the fuse is to be always the weakest element. Having a 20A fuse in a circuit designed for 10A is no protection, it's a fire hazard.
As Steve recommended, fit the prescribed fuse. If it blows, check for cracked wires, etc. Play it safe.
88 164 2.0 Turbo 4C - 93 Citroen C15D - 94 Citroen ZX's, 1.4i, 1.9D - 96 Citroen Saxo VTS - 98 Citroen Jumper - 99 MB E220 CDI W210 - 2001 Renault Clio