Regarding using the sleeper to Glasgow for work; I usually have meetings near East Kilbride and Paisley and arrive for 9.30 start (by train and sometimes taxi) having had a shower and breakfast in Glasgow. The sleeper gives time for a full day of meetings, an evening in Glasgow and back into work about 10am next morning. Occasionally I hire a car from close to Central Station. It’s ideal for me.
If I only had morning meetings I used to get a day train back via Edinburgh and enjoy lunch in the restaurant car. Now I make the most of the time and travel somewhere once the meeting has finished (Brodick, Troon, Dunoon, Rothesay for example – even Corrour once) and get the sleeper back from Glasgow, or I go on somewhere and take the Highlander back (often Pitlochry, also Inverness, Aberdeen, Stonehaven, Bridge of Orchy).
So whether purely for business or combining business and the pleasure of exploring Scotland by train, I find the sleeper to be a brilliant way to travel.