When you call to dispute a charge, your credit card company contacts the original merchant. They can either request information from them about the purchase, or just immediately side with you (a chargeback). If they perform a chargeback, the money gets removed from their merchant account and deducted from your bill, and they get hit with a chargeback fee.
One of the reasons merchants collect the signature is to have more data to give to the credit card company during an inquiry, or so they can try to dispute the chargeback. If you claim you never made the purchase, having your signature on a slip helps the merchant with the dispute, as would having you on video signing for it. Credit card companies side with the customer a vast majority of the time, but if the merchant has reasonable proof that you knowingly made the charge (which might include that signed slip), the merchant can win those disputes.
Previously not having a signed credit card slip usually meant the credit card company automatically sided with the customer over the merchant. I doubt dropping this requirement will make it easier for merchants to win chargeback disputes, though.