as a young engineer we still had Kelly rigs and some two or three years into my career we installed a top drive. One of my experienced supervisor saw three major problems with the TDS:
1) thread damage due to stress on the threads when using the TDS for make-up und unscrewing, if the driller does not exactly keep the balance
2) the string not being able to turn freely when pulling out of hole and running in hole - could be an issue with hole spiralling or, which I think more likely, the issue with stabilizers. Anyway, the string could move freely through hole sections when allowed to turn freely, where a TDS rig would see either overpull and/or potential backreaming.
3) the backreaming option makes things quite easier as sections with hole problems could easily be passed through, but - and this is something that Peter aims at - hole quality does not get better with the excessive use of backreaming. This was one of the issues of the "good old times" that before pulling out of hole you made damned sure that the hole is in good condition.
Drilling and tripping practices consequently changed with the use of TDS's as pumping out or rotating out of hole became the common option. This is still the issue of a good supervisor/experienced driller to adjust the drilling/tripping procedures in a way to arrive at an optimum output!