Why are there springs under the heated bed

So you can adjust the build platform. The bed isn't threaded, it relies on the spring pressure to push it against the top of the bolts.

Just make sure you start your z-height and levelling with all 3 screwed down, then they shouldn't need to screw in more than a few turns to get it even.. if you start your adjustment with them already at half way, then by the time you're done they will be much much higher...

All you can do is try it for yourself and see I guess... But it will also mean that if you have a whoopsie with your bed height being mis-set, you risk then doing serious damage to your x-carriage or nozzle tho..

Personally, I'd just screw them all the way in, and like I suggested, adjust the height/level from there - my bed only sits a few mm's above the sides of the platform... about the same as my wooden platform did... *shrug*

The springs are also there to have a little give going up and down on the bed. The nozzle presses down on the bed when it glides over parts that have already been printed and those parts aren't entirely flat. If there's no give, the nozzle has a good chance of crashing into the printed plastic and skipping steps.