I used to do that with a vintage 70's sportscar… later learned that it was pretty bad for the long-term life of the transmission so had to train myself out of it.
It's gentle on the transmission and clutch if you rev match on the downshifts.
Or see the hill coming and downshift before it is needed
Also fun! Half the fun of a manual for me is double-clutching (totally not necessary unless you have no synchros but it's a fun challenge) and nailing the rev-match on a downshift.