We vary according to distance needed to travel. If the landfall and the destination is planned before dark we accept whatever speed will get us there in a timely fashion although anything below 3 knots is generally considered engine time. The only variable to that would be when we only have around 5 miles to go and time to do it in. We can spend the day starting the engine a number of times for a short time shutting it down when the wind cooperates.

If we have 50 miles to go it just seems dumb to travel at 3 knots when we can go 7. We purchased our vessel not as a sailboat but more of a vessel that gets us to a destination (preferribly) under wind power but the engine as a means to the destination has equal importance. Quite often we will motor till time and distance works and then sail at whatever speed the Earth gives us even if it's 2 knots although I generally feel anything less than 4 is slower than I wish for.

On a multi day passage as long as we're going over 3 we take it saving the fuel for less than that speed

Of course, a short day sail is out of those parameters. On day sails it's about comfort. If the seas are comfortable at 3 knots and we don't have a destination except for 'out & in' 3 knots or even 2 1/2 can be a wonderful speed. Less than 2 is generally agonizing.

Sailing and boat speed is a complicated concept or equation for us.