Prevents your bed leveling wheels from being moved out of position unintentionally when you bump them while still allowing access when you do want to adjust them by reaching under the shields.
Slide-on version just snaps around your bed springs. Might be affected by the type of spring you have or how tight they are. Not very secure but should be good enough. It is for me, at least.
The screw version is more secure but you need to take your bed from the carriage and put the guards under the springs. Full disclosure: I have not used These. These are the first version I made then made the last second realization to make the other one. But I see no reason why they shouldn't work.
These were made with the Ender 3 S1 Pro in mind so can't guarantee it working the same for other printers.
The author marked this model as their own original creation.