The grids sit a bit off the bottom of the sink and they help cushion dishes and glassware from breakage while being washed. They also let you drain glasses if you place them there upside down.

Silgranit is a really nice sink - but any solid surface can crack if you try hard enough!
Think of a heavy Staub or LC dutch oven dropping onto your granite or into your sink...
Stainless might dent - but stone is likely to crack..
I don't store my grids in the sink - but when washing heavy items, I do drop them in the sink.
I can vision too many germs living in the feet!

I use one in my silgranit prep sink for various reasons, but nothing to do with protecting my sink. Some random uses:

* If I use a colander, I set it on the grid to drain (with confidence that the water won't get on the food.)
* I also use the grid for cleaned pots or bulky items to dry.
* I put hot items, like pots or pans, on the grid to cool down. Similarly, some frozen items are placed there to thaw.
* During a portion of the summer, that sink (with grid) are dedicated to cleaning/holding veggies from the garden.
* DH puts his hand towels on the grid. I guess that is because they are out of sight but able to air out/dry.

I love my SIlgranit sink and grid, and use it similarly to the way Lolauren does. My grid was included with my sink, and I was not sure I'd like it but now that I've used it, I would always choose to have one.