it makes the process much easier if something happens to your mediabase or if you need to make different ones.
You only need to analyse a track once, wither it be by playing the song in a player or using the analyse feature... you will always have the information no matter what media base is loaded...
The only reason you will need to re-analyse the files is if you reinstall Mixvibes without backun up the Peak directory from C:/Program Files/MixvibesProducer/