Are there any situations where it's beneficial to disable altitude reporting in TCAS? Having altitude reporting enabled persistently seems like a pretty common-sense thing to do -- it enables RA in addition to TA, the benefits of which are fairly obvious. That said, most of the common transponders installed in GA and commercial aircraft have either the option to explicitly turn on (typically on GA) or to explicitly turn off (typically on commercial) altitude reporting.

Are there any normal or abnormal flight conditions which would make it impractical, unsafe, or impossible to have altitude reporting turned off?
The only time it would make sense as a normal or abnormal procedure to turn off altitude reporting is when your static encoder system is reporting no or incorrect altitude information. Especially in today’s world of mandatory Mode C and/or ADS-b in certain airspaces. ATC in those airspaces may have you cycle your system temporarily. Or, they could have you permanently  turn it off while you either land as soon as practicable or vacate the airspace until the system is repaired.