If the dock's floating then I want my lines fairly snug, but not tight. Fenders (not bumpers) take up the slack. The idea is that the lines take up boat movement away from the dock
and the fenders absorb movement when the boat's heading for the dock
. The idea is to moderate the amount of boat movement.
If I'm in a area with significant tide swings then I tend to leave the bow and stern lines looser but have the forward and aft spring lines fairly tight. In most cases, these spring lines are longer than the bow and stern lines and have a bit more stretch.
It takes some tweaking but I'm looking for snug, not tight, bow and stern lines at high tide, and less at low (most places I frequent have higher high tides than lower). I also use double stern and bow lines, either to different cleats
if I'm sharing as slip or, to cleats
on the other dock if I've got the slip to myself.
Don't forget chafe gear
and regular checking of the lines.