What you actually get when you convert an MP3 to WAV
MP3 and WAV in plain terms
MP3 is a compressed format from the early 1990s. It makes files small by discarding sounds that are hard to hear. WAV is a container, created by Microsoft and IBM in 1991, that usually holds uncompressed PCM audio: every sample, nothing removed. That is why a WAV is big and an MP3 is small.
It will not sound better, and that is fine
The detail MP3 removed is gone for good, so a WAV made from an MP3 sounds the same as the MP3. What changes is how the audio is stored. Nothing more is lost when you trim, layer or save the WAV again, which is the whole point.
Why people still do it
Some audio editors and hardware samplers want WAV. Video editors prefer it for voice-over and music beds because it avoids re-compression on export. It is also the safest hand-off to a mastering engineer, and many sound libraries and game tools request it.
Plan for a much bigger file
A three-minute song at 128 kbps is about 2.9 MB as an MP3. As CD-quality stereo WAV it is about 32 MB, roughly eleven times larger. Standard WAV files top out at 4 GB, which is about six and a half hours of CD-quality audio, so that limit rarely matters for music.
If you have the original, use that
If you still have the CD rip, project file or master recording, export your WAV from there. A WAV made from an MP3 is simply the MP3’s sound in a bigger box.
Edit and mix in WAV, then export to MP3 once at the end. Every extra MP3 save adds another round of loss.