There are multiple reasons to do so: re-using when you play this Pokmon on your Bench Abilities, healing a damaged Pokmon, saving an easy target (like Lumineon V) from a potential KO, or just managing Bench space
The materials are other permanents you control and/or are cards from your graveyard
For example, Sarkhan, the Dragonspeakers first loyalty ability turns it into a dragon until the end of the turn
The Game Edition enhances the experience by including a download code for the original PC version of Final Fantasy VII and a special promotional version of Cloud, Midgar Mercenary featuring his iconic, blocky character art from the 1997 PlayStation classic
Each opponent sacrifices a creature of their choice
Just think, before 2010 the mechanic was limited to only working with other creatures with the same bands with other ability