after about six months, a properly crimped wire has an ipedence of roughly 0.03 ohms, due to oxidation (it gets worse as time goes on). this doesnt sound like much, but consider the fact that from the battery to the amp there can easily be five or more crimped connections through distribution blocks and so forth.
lets assume five connections of 0.03 ohms, for a grand total of 0.15 ohms. for a 50w x 2 amp, the maximum current is approximately 17 amps. this rusults in a maximum voltage drop of 2.5 volts, and a reduction in maximum power over 30 percent. remember, this is due to the connectors alone, and on top of any additional losses in the wires themselves.
crimping and then soldering results in an ipedence of 0.01 ohms per connection. this number does not degrade over time. for our example, this would limit the maximum voltage drop to 0.85 volts, and the reduction in maximum power to 10 percent.