This is the direction where the trade-off is real
Unlike converting a lossy file up to WAV (which gains nothing), converting an uncompressed WAV down to MP3 is where a genuine, meaningful trade-off happens — you're starting from full-fidelity source data and choosing exactly how much of it to discard in exchange for a dramatically smaller file. This is the conversion direction MP3 was actually designed for, and it's why WAV-to-MP3 is far more common in practice than the reverse.
Choosing a bitrate that matches the source's purpose
A WAV file that started as a professional music recording deserves a higher bitrate (256-320kbps) to preserve as much of the original fidelity as reasonably possible in the smaller format. A WAV file that's actually spoken content — a recorded meeting, a voice memo, a lecture — can drop to a much lower bitrate (96-128kbps) with no perceptible difference, since speech simply doesn't carry the frequency range and dynamics that music does.
Matching bitrate to actual content type, rather than defaulting to one setting for everything, is the difference between an efficient conversion and one that either wastes file size or sacrifices quality unnecessarily.
Keep the original WAV if you might need it again
Because this conversion direction discards information permanently, it's worth keeping the original WAV file around, at least until you're confident the MP3 output meets your needs — the WAV can be re-converted at a different bitrate anytime, but once you've deleted it, an existing MP3 can't be converted back up to recover the discarded detail.
This is exactly the archival-master-to-distribution-copy pattern
This conversion mirrors a standard professional workflow: keep an uncompressed WAV as the archival master (the version you'd return to for future edits or higher-quality needs), and generate MP3s specifically for distribution, sharing, or everyday listening where file size and universal compatibility matter more than absolute fidelity. Thinking of the WAV as the source of truth and the MP3 as a derived, purpose-built copy avoids treating either one as disposable when it isn't.