Yes.

$0.02/GB, $0.3/kWh, 15 Watts AMD mobile chip -> worth it if more than 500 kbit/s are saved. I observed significantly more than that using hardware-accelerated encoding to H.265/HEVC .

At 2 dollar cents per GB, 30 dollar cents per kWh and using a 15 Watts AMD mobile chip, re-encoding would save money if more than 0.225 GB are saved per hour or around 500 kbit/s.

Encoding to H.265/HEVC I observed up to around 20000 kbit/s being written to disk for a 30 FPS movie. If the new movie is smaller than the older one by even a few percent, the condition is satisfied. Without hardware acceleration, around 1300 kbit/s are written to disk, still enough in most cases.

So you've looked at the increasing storage prices in disgust and thought you should get rid of unused data on storage devices you already own instead of buying new storage. You rummage through your files and encounter a couple of humongous movie files. You think that technological progress surely must've blessed us with more efficient video codecs by now and want to re-encode these files to free up space. But is it actually worth it? Re-encoding requires energy and thus isn't free.

Recently, you were able to buy hard disk space for around 2 dollar cents per GB and electricity for maybe around 10 to 30 dollar cents per kWh. I used an AMD chip to re-encode a movie using hardware acceleration and that chip is a mobile chip that supposedly uses at most 15 Watts. At the higher electricity price, this device would consume 0.45 cents per hour in electricity. For re-encoding to be useful, it must save more than that in space. At the mentioned 2 cents per GB, this would be true if more than 0.225 GB are saved per hour or around 500 kbit/s.

I encoded to H.265/HEVC and the AMD chip was able to write up to around 20000 kbit/s to disk when encoding a 30 FPS movie. As long as the new movie is even slightly smaller than the original, the cost saving condition is satisfied. When not using hardware acceleration, the encoding speed drops to around 1300 kbit/s, but that is still more than enough in most cases.

So, in the current situation you can rest assured that re-encoding movies to save space is not a fool's errand. But this calculation ignored your time cost. If you spend even just 1 hour doing this (not very realistic if it's many movies) , you would have to save hundreds of GBs to justify the time expenditure. Ignoring that, you would have to use a really inefficient CPU (central processing unit), suffer even higher electricity prices, witness a further precipitous drop in storage prices (while in reality the storage prices are currently rising) or try to encode from an already very efficient codec to the same codec to lose money re-encoding movies.