FLAC to OGG: a smaller, open-format copy
Why the pairing makes sense
FLAC and Ogg Vorbis come from the same open-source family. One is lossless and large, the other lossy and compact. Many people keep FLAC as the archive and use OGG for portable or in-game copies.
The size saving
A 40-minute album is roughly 230 MB as FLAC and around 50 MB as typical-quality OGG. That is about a quarter of the space for a loss you are unlikely to hear on earbuds.
Tags between the formats
FLAC and Ogg Vorbis both use Vorbis-style comments, so titles, artists and albums normally transfer cleanly. Cover art is less predictable, so check a file before you convert a library.
OGG or MP3?
OGG is open and efficient, and many engines and Android players handle it well. MP3 plays on more devices, including many cars and Apple products. If you are not sure, pick MP3.
Keep the FLAC
Lossy conversion is a one-way trip. The FLAC remains your master for any new copies.
Making game audio from a lossless soundtrack? Convert once from the FLAC, and avoid re-encoding the OGG later.