question

It is usually only used in Lead Acid Flooded batteries,

as when these batteries sit for a long time the liquides separted. ie the acid and the water, The equalization mode puts the battery voltage up and re mixes the liquids as the battery gase the liquides mix

As Paul B said equalization is for Flooded Lead Acid batteries, as the batteries are cycled the individual cells can become unbalanced (each cell be in a different charge state). The higher voltage used in equalization helps bring all cells to the same state of charge. Manual equalization just allows you to start the process. There is a great book on Victron's website under downloads/Technical information called Energy Unlimited if you want more information.