What are fuses used for?

Some fuse holders are square and require a push-in for release. Others are round and require a push-in with a twist before they can be pulled out.

Thanks again!

After trying a few different brands of high end fuses on my McIntosh C2500 tube pre I have come to the conclusion that there are better ways to spend the money (like giving it to the homeless).  Either my system has such high resolution that they aren’t needed (doubtful), or it’s snake oil.  I go with snake oil.  

I tested some "premium" fuses a while back after disputing the insane hyperbole attached to them by a few shameless salespeople...I figured it would be interesting and I had access to a pile of 'em...I found them to be absolutely useless relative to SQ, and some were actually rated improperly and blew in a power amp. 

OK, Wolfie, I’ll give you that - they didn’t work for you. So it’s what, you against 40,000? The smart money is on the 40,000, not some pro audio layabout.