Why convert to WAV at all
Some older audio software, specific hardware devices (certain DJ equipment, older samplers, some car and home audio systems), and professional editing workflows either require or strongly prefer uncompressed WAV over compressed formats — WAV's simple, uncompressed structure makes it universally readable without needing a decoder for a particular compression scheme, which is exactly why it remains the safe fallback format for compatibility-sensitive contexts.
Audio editing is the other common reason: working with uncompressed source data means edits, effects, and processing operate on the full, unaltered sample data rather than something already run through lossy compression, which matters for multi-step editing chains where compression artifacts could otherwise compound.
The one thing conversion can't undo
Converting MP3 to WAV changes the container and encoding format, but it cannot restore audio detail that was already discarded when the file was originally compressed to MP3 — MP3 is a lossy format specifically because it permanently removes information the format's algorithm judged you wouldn't notice missing, and that information is gone, not just hidden. The resulting WAV file will be uncompressed in format but capped in actual audio quality by whatever the original MP3 compression preserved.
This is worth knowing before converting specifically because it prevents a common disappointment: expecting a WAV conversion to sound noticeably better than the source MP3, when in reality the WAV can only ever sound exactly as good as the MP3 it came from — just larger.
When the conversion is genuinely useful anyway
Even without a quality gain, converting to WAV solves real compatibility and workflow problems: getting a file to play on hardware that doesn't decode MP3, feeding an audio editor that works better with uncompressed input, or meeting a delivery requirement that specifically calls for WAV format. The value here is compatibility and workflow fit, not quality improvement — and that's a legitimate reason to convert even knowing the audio content itself won't improve.
File size goes up substantially
Because WAV stores audio uncompressed, converting from MP3 typically increases file size by roughly 5-10x depending on the original MP3's bitrate — this is expected and simply reflects the removal of compression, not any error in the conversion. It's worth accounting for this size increase if you're converting many files or have limited storage.