The alignment tool will prevent the friction plate from dropping out as you loosen the clutch housing from the flywheel. Just do the bottom bolts last and have your hand at the bottom to prevent it from falling.

You don't *NEED* one for installation... the transmission input shafts are typically chamfered and as long as you are close you have get the input shaft started, and if the splines don't mate then pull the clutch bearing arm to release the friction plate and turn it.. you can feel when it engages.

It is MUCH easier with the alignment tool, but not terribly difficult if you don't have one.