War stories aside;
Mechanical (crimping) connections are formed by plastic deformation of the metals. The resultant connection starts out tight and then loosens over time. Once the connection loosens slightly, its conductivity plummets; this is why high power DC connections often overheat - they become poor conductors, and the current increases over time - until the connection is hot to the touch, or your boat burns to the waterline. Exposure to humid air and salt increases oxidative degradation. Crimped connections are a perfect candidate for crevice corrosion - the interstitial spaces between wires and between the wires and the connector pull in water by capillary action. Oxidative and galvanic corrosion increase the looseness of the connection.
Vibrations, and harmonic frequencies of all of the primary vibrations on a sail boat concentrate naturally at stress risers - the crimped connection is a huge stress riser, and will often fail through vibrational induced brittle fracture at the connection point.
Silver solder, with at least 3-4% silver, and rosin core flux, makes a poor mechanical connection (it is not glue) and an excellent electrical connection. A properly soldered mechanical connection is immune to crevice corrosion, it can corrode on the outside surface only. Vibrational analysis has proved over the last century or so that a properly soldered connection will last many orders of magnitude longer than a mechanical connection.
Many of the horror stories of soldered connections are no doubt from uninformed boaters using acid core solder that he had left over from the plumbing project to solder wires. The acid flux will eat the copper and tin in about a week. And of course, it is perfectly easy to make a solder joint look great and be useless; cold solder joints are difficult to detect - you have to know how to solder. Mechanical joints are easier to test (pull on the wire) but you will never make acceptable crimped connections with the Wal-Mart crimper that came free with the 12 feet of 12 gauge wire.
The best of both methods can be had, and the drawbacks of each reduced, by soldering a connection first and then adding a mechanical connector.
The advantage of the ring, spade, etc. mechanical connector is that it makes a much better connection to terminal blocks and connection to devices than a soldered wire, and it is removable.
The soldered connection prevents loosening of the mechanical connection and corrosion beyond surface corrosion.