I was able to find the exact verbiage on Amazon for a Toyota gas cap. It implies that you will get a CEL (check engine light) and you could, which could cost you money to get it checked out.
Here is the listing:
Genuine Toyota (77300-33070) Fuel Tank Cap Assembly
Genuine OEM Toyota Gas Cap New in Original Packaging with Seal.
The typical life span on gas caps is 5 - 6 years.
You can prevent unnecessary service costs by replacing the gas cap on
modern vehicles before they go bad and the check engine light appears
However, I had a CEL come on, due to a tiny vacuum leak at the gas cap and I drove it for quite a while, over a year, with no ill effects. I didn't know that the solution was a new gas cap and didn't want to pay the expense of having someone locate the leak. I found out later the gas cap was the usual issue and the light went off when I replaced the gas cap. If the light comes on over something like this it isn't going to hurt anything.
Where I live in St. Louis, AutoZone, Oreillys, and Advanced Auto give you a free reading for a CEL, but I know shops were still charging for readings if you asked for one.