The reason why crimping is by far the superior method of making a good electrical connection is that a properly compressed connection (that means, the right tool, for the right size connector and the right pressure applied to the crimp) will make the wires & connector pretty much become one. Some people refer to this as a "cold weld".
This is what a proper crimp looks like if you cut it half
As you can see, the wires & connector become one. It eliminates all voids between wires, thus keeping any air out. This prevents corrossion, which is the #1 problem in electrical connections. Corrosion increases the resistance of the connection, which leads to overheating.
Check out this article "This is NOT a crimper"...good information
This one also has a lot of good information.
While soldering does "seal" most of the connection area, mechanically, it is a fairly weak connection, especially with all the vibrations on a boat, which add to crimping being better.