Depends what you're playing from. I don't have a terabyte of storage on my phone and I'd like to store more than just audio books and music. If you've got a desktop with magnetic storage then sure.

I'd also be curious if you can tell the difference between a 128 kbps Opus and a lossless flac file (in a blind test of course, easy way to test yourself: cp a.flac $RANDOM.flac; cp a.opus $RANDOM.opus; play both with cvlc or something, make your guess, then look at the file size to get the result, repeat at least five times). I could see the argument for having a lossless copy somewhere, just in case you get better audio playback equipment in the future, but for a hot copy (especially on a mobile device) I'm not sure flac is beneficial.