Its rare we ever used client compression..

Generally speaking the only time it makes sense to use client side
compression is when you have network bandwidth concerns and want to
reduce the load on the network (i.e. you have limited throughput between
the client and server.. a laptop backing up through the internet or a
server having to go through a slower firewall).

I could also see maybe using it if your disk storage pool was limited in
size and nightly backups were causing migrations to kick off because you
don't have enough disk storage to hold your backups. Turning on client
compression would pre-compress the data and would help with that.

Ultimately the amount of space it uses on the tapes is going to be about
the same.

Gerald