big bore TCM
Not recommended turning backwards on the larger TCM engines with the spring starter drive. The spring has been known to catch and scrape metal from the clutch or brake or damage to the spring itself.
Turning forwards is OK and with the TCM engines and I do it regularly on the first flight out in the morning just to keep an eye on what is happening with the cylinders and the impulse couplings. I do a lot of back country operations with no engineering support other than what I can do myself so I like to look after my machine so I don't have to walk out of the hills. I only fly the one aircraft that I own and maintain myself, no one else flies the aircraft.
For a new pilot I don't think there is much point turning over the engine as it has taken years of fixing and flying to know what to listen and feel for so as a regular practice it is probably not worth the time if you operate only in civilization with engineers and workshop support.
The one rule I was taught both as a pilot and as an engineer was that the prop (engine) is always live whether the mags are on or off and to treat is as such - always!