So a guy has million or so feet of THHW #6 copper. Wants to run about 90 amps to a sub panel in conduit.

What are code or safety reasons for running 3 or 4 of these seperate conductors per line and connecting them with a in line splice to a large single cable at the panels, or winding and soldering them into a single lead at each breaker connection?

And if its a no-no in the book, can you say the practical reason why? Besides being a lot of extra labor.

And try not and simply say don't say trade it for the "right" cable.