[NAME] is spot on, those are used for vibration dampening. It will not cause a problem if you do not use them on the new drive. None of my Dell laptops ever had them and there was no excessive vibration noticed.
Dear all,   I hope this question is valid enough to be posted on here: in regards to installing a new hard drive into a DELL XPS 15 7590, is it essential to also install the hard drive (rubber) covers during the process?  I ask this question, as the hard drive that I have installed is a bit too big for the covers to fit, so without the covers, the HDD fits fine along with the metal cage.  I hope there aren’t any potential risks associated with removing the covers and keeping the HDD in the laptop as it is. Please let me know - it would greatly appreciated. Thank you.    
Are Hard Drive Covers Essential?