Replacing a cutting mat is like losing an old friend, so many memories.
When the grooves are there, it won't make a difference how sharp your blade is because the threads get jammed into those spaces. Then the grooves will dull your blades because there's not a solid surface for it to roll along.
Or, you'll have to position your fabric on an "uncut" portion of your mat......or, you'll be forced to shop for a new one, which you may also fall prey to the temptation of so many fabrics screaming for you to buy. Warning: it may cost you more than you thought. :P