It's not that the fingers (levers) are under a lot of tension.
As you bolt the pressure plate to the flywheel, the force of the pressure plate bottoming out on the disc forces the fingers down, or forwards, torward the engine. Conversely, as you unbolt the pressure plate, you'll see the fingers rising, or moving towards the rear of the vehicle.
The concern is that without the blocks in between the fingers and the pressure plate frame, that the pressure plate housing (the part you bolt to the flywheel) will be too far away for the short pressure plate bolts to get started. I looked on YouTube for a video that explains this better but was unsuccessful.
If you're not reusing the old clutch, then don't worry about it. If in the future, you're reusing the pressure plate, then use the blocks.
The above scenario is why many race clutches are sold with advertised specs for the "installed finger height"-because the fingers are in different positions, installed and uninstalled.
Also re: Gimpy's comment. I can't read dry humor over the internet because I'm colorblind, but how do you get to the flywheel bolts with a clutch disc in the way?
EDIT: I see while I was typing this, Gimpy responded. For clarity, you can not remove the flywheel without first removing the clutch assy.