You should do this to ensure that your tiles are properly acclimated to the room's temperature before installing them.
Dirt and debris will interfere with proper tile adhesion if the floor is dirty or soiled.Tape a "X" in the middle of the room, and you're done. Your peel-and-stick journey begins here.
Tiles should be laid down in the pattern you intend to use. You'll save a lot of time and effort this way.
It's up to you how far you want to go. At the very least, till you've completed the space. You'll need to chop them down to size to You'll need to chop them down to size to make room for the tiles that don't quite line u. But other than pushing the tiles down, peel-and-stick installation is essentially a one-step process.