An endless selection of plumbing parts. Whatever I need, I'll find it here. Often I only have a vague idea of how I'm going to do something, but being able to search through these shelves and dry-fit parts together tends to unlock solutions I hadn't even thought of.
Then there's also the immense calm I feel being in a space where everything is neatly organized in its dedicated places.
I don't see what's crazy about it. PEX has the same outside dimensions as copper pipe, so the fittings are cross-compatible. The only difference is that with PEX you need to use a support sleeve inside the pipe to stop it collapsing under the olive - just like with copper that has gotten hot from soldering. I prefer joints that can be undone.