Since solder is such a poor conductor, why use it?

I used to manufacture my own cables and quickly realized that solder was no good...I crimped all my cables

Stringreen, is there not a problem of oxidization with crimping?

Al's first response is excellent, he obviously knows what he's talking about.

It's best for the materials being soldered to already have a good mechanical connection before soldering. The solder just holds it in place.

However, solderless set-screw connections do tend to sound best but the difference vs using good lead-free silver solder like WBT or Johnson is slight. The best RCA plugs imo, WBT 0102, are the best despite requiring soldered connections.

Davec113, yes, solder is good for holding in place, but so is super glue. It is not conductive, however, and may harm the cables. However, the solder even for tightly crimped wires would flow between the wires.

Use a length of solder wire in a circuit and listen to what you've got. Crap!

The best connection is probably wire wrap. With wire wrapping. Some audio gear made in the 1960's and 1970's used this approach, but for cost reasons, it is no longer used. The connection is physically very strong and completely gas tight (no oxidation at the physical point of connection). See the following:

https://en.wikipedia.org/wiki/Wire_wrap