Eddie101 You will soon learn that discussing fishing line preferences is like asking do you prefer blonds, brunettes, or redheads.

I know competition fly fisherman will boil their mono leaders to soften them. The softer line has less influence on the nymphs and  creates a more natural movement in the water. 

I’ve never even heard of it before. 

Saltwater fishermen are known for boiling thick monofilament leaders to make them more supple. I think it is a waste of time to boil monofilament line but people can do whatever they feel helps them.

212 degrees (100C) is above nylon monofilament line elastic modulus and will drastically weaken it's strength permanently. You basically ruin the mono line. 

Tom

A quick google search shows that it is in fact a thing but I don’t think boiling water is actually used. Just very very hot water, but I wouldn’t recommend it anyways

Buy better line. No way I'd be taking the time even to put all mine in warm water before a fishing trip. Good line should be manageable enough to fish with without doing anything extra.