Libraries that have survived a few computers are rarely tidy. There's WMA from the Windows Media Player years, M4A from an iTunes phase, WAV from something that was once burned to CD, FLAC from a brief audiophile period, and OGG from who-remembers-where.
This tool flattens all of it to MP3 at a single consistent bitrate, so the whole collection finally plays in one place — phone, car, speaker, anywhere.
One bitrate for the whole collection
Standardising is the point. A library where some tracks are 320 kbps and others are 64 kbps has audible steps between songs and unpredictable file sizes. Picking one setting — 192 kbps suits most collections — gives you a library that behaves consistently and fits predictably on a phone or a USB stick.
Where you have genuinely lossless sources such as WAV or FLAC and want to keep them that way, convert those separately to FLAC for archiving and generate MP3s for portable use from them.