Some transmissions can handle being towed and many can not, they don't oil properly if just the output shaft turns. The shop or operators manuals often explain.
So it's just the safer bet to remove axle shafts or pull the driveshaft.
For real short distances it might not matter in most cases, for a little longer you can just let the towed vehicle idle in neutral to oil the transmission while towing. Anything more and just as well remove shafts, less risk and wear and tear on things.
Particularly an unknown vehicle. Tims COE had few quarts of water in the differential when I got to it, which I drained. With shafts removed all I cared about was wheel bearings which I washed and greased. Didn't harm the differential as it never turned and Tim could deal with that at his leisure.
