My posts may have been misinterpreted. I am not against after market fuses and have been using them for some years. Right now I have 5 x SR purple waiting to be fitted to my amps, replacing SR blue fuses, which at the time had a significant positive affect on sound quality. In other words, I recognise and value the surprising improvements that they can make.
I can understand when it is stated on this forum that fuse manufacturers have recommended going up in fuse value to prevent them from popping, because it would reduce the number of returns or replacements they would need to make. It sounds like a commercial decision on their part. What I cannot find on the internet is positive corroboration from them that it is the correct thing to do for equipment that states a specific value of fuse.
I can also understand that an individual would increase the rating of their fuse in order to protect their $/£ fuse investment after reading comments about failure rates. Human nature - if you read a posting that says increasing the fuse value works, go for it because it worked for others - but is that the correct thing to do electrically?
What I cannot understand is why an equipment manufacturer would specify a fuse value, and people assume that it is good to ignore that and follow suggestions on a Forum that contradicts this. What do the equipment manufacturers say? To read on a forum a justification which says 'they leave lots of headroom' does not really cut it. To say that it depends on whether or not the equipment has start up surges and how it handles them, is surely something that the equipment manufacturer would have considered before specifying a value.
What is the point of specifying fuse values if they are just to be ignored?