In some cases it had to do with the duty day. You could leave Manchester for example, coach toTeeside, and still have enough duty hours to go to southern Spain.
So the aeroplane left Manchester early for rotation to Spain and the W destination, landing there around mid day. You left Manchester by coach with a crew mid morning and arrived at the W, to pick up the aeroplane and fly the second rotation. This gave 2 to 3 hours coach, and 8 hours to Spain and back, or an 11 hour duty day with 2 sectors. No problemo.
The coach at the W would then take the early crew back to base.
But if the W was a Canary or Cyprus, then it would be a position to the W the night before. Usually the coach stayed at the W, and when the inbound crew landed the next afternoon, it would take them back to Manchester. A long duty day for them, but it was after flying and was usually compensated for by an increase in the required rest period. This also happened if the UK part of the W was over 4 hours from your base.
There was to my recollection very little positioning by air after the crash in Glasgow, and in later years when we had to start and compete with the low cost carriers. There was also the problem when the work horse became the 757 (and 767 long haul W patterns) since there was a crew of at least 7 and some times 9 or 10. Air taxi seats and payloads were pushed with 8 crew, their flight bags, and suitcases. Anyone who has travelled with a female cabin crew to a night stop will remember what that could weigh!!
Even positioning by schedule airline was significantly more expensive than a coach when crews of that number were involved.