When I have to get there I concentrate on getting there. If it is 30 miles and there is a lot of tacking I will motor mainly because I am feeling lazy... usually either the day before or the day after is a race in the opposite direction often in light winds in wrong direction - I get my sailing in then.
If I am short handed and the winds don't favour a nice sail or it is a short one or on the nose then I motor. If I have adequate crew more often we run the sails. If windy and behind and short handed just the main or if I have a good crew then the spinnaker. I absolutely hate wing on wing for long distances ....
Finally - if sailing is faster we sail.
Two weeks ago had a race starting from a club 34 miles from our marina. It was 8:30 at night when I left alone and not much wind. I motored. The next day was race day (40NM) and 20knots wind. We sailed of course and it was a blast flying the chute in 20+ knots! (there ws crew of three and no kids). The Sunday I left the dock at 4:30AM under motor and when the sleeping crew woke up 3 hrs later we had rounded a cape directly into the wind (was forecast to die in the morning) - we continued to motor all day. 66miles. long day.