There are plenty of free recording programs online that will save locally to your PC and not cause lag. Personally, I recommend OBS: Open Broadcaster Software | OBS.

These videos will be very important in case you are scammed or believe you were wronged as a renter. Without the videos, you could be booted off the account at any time, lose your items, and be unable to prove that this has occurred.

Please note that you must provide video evidence in order to file a scam report against an account lender booting you off. Extremely damning evidence (i.e., the lender admitting to booting you off) suffices, but in a vast majority of cases, a video will be necessary.