There's probably a NASA workmanship standard out there somewhere that details it, but Mjolinor is correct in how stranded wire should never be tinned when the wire will be crimped or tightened under a screw head.

Yes, it appears to provide a more solid initial feel for the crimp or the screw terminal. The problem is that solder isn't as solid as it seems. When put under pressure (as in a crimp or screw terminal), the solder will slowly creep and flow out of the way, loosening the connection. It's just a matter of time - maybe months or more, but it will eventually lead to a poor connection.