Dont forget to fuse things - never run wires from the fusebox without independant fuses 
There are fuses in the fuse box... lol
If the wire shorts after the fuse box the fuse will blow.
Its neither safe nor recommended to add further strain on the fuses in situ. Any new systems should be taken from the left hand side of the fuse box and fused independently.
If you take a permanent live from the right side to the HU you are allowing the chance for 25A / 35A to pass down a wire designed for 10A.
Please think about advise before handing it out. I build looms and am a wiring trader on here. Not just a TMF+ Member.
Correct me if I'm wrong, if the wire draws more current than the wire can take the fuse will blow anyway (because the fuse is rated to the wire) so its protected away, so it wont even be able to draw 25.35A? So what difference does it make?
especially since radios draw very little power anyway and many, many people have wired it like that, seen as that's how it would have come standard if it had a radio (feed taken from the right side of the FB)...
If you run a 25 amp fuse, connected to a wire rated a 10 amps, the unit could draw 22 amps for example due to a fault.
This could cause the wire, and ultimately the car to catch fire.
Just because lots of people have done it doesn't make it right.