I think it depends on your expectations. I had a black cast iron Kohler sink. Didn't have the grids at the beginning the sink had lots of scratches from pots, and it sort of bugged me for a long long time.

Then we renovated, and now have a stainless sink. I wanted to get those grids right away, but Ticor didn't make the grid for my sink--it was "coming soon". So, I decided I would just forget about it, let the patina do it's thing. Now, I'm happy that I don't have a grid. I don't have to lift it to clean under it. I also think if there was one, I would have a certain level of expectation that the sink would not get scratched--and well, that probably can't be avoided.

I like my big sink, and I like the scratches that are coming naturally to it.

I have a large single bowl ss sink with a grid, and no disposal. I keep a little mesh screen over the drain to catch crud (so much easier than the typical drain plug.) I like (1) draining pasta without water backing up into the colander. (2) washing or filling pots without blocking the drain hole. (3) it raises the effective floor of the sink a bit for my back. (4) you can use it to drain washed dishes directly in the sink and (5) it is a more level surface than the canted surface of the sink. I wish it fit in my dishwasher because it does need to be scrubbed regularly or it will get gross. The little rubber feet create teeny cups that are always full of water.

I'd like to try a grid but the one that is made for my sink is $240! I'd rather buy my kid a new bike and have a scratchy SS sink!
Why on earth are some of them so expensive?

I took my grid out. Our ss sink is the prep sink, and we don't have a sprayer there, so cleaning requires wiping every time, no way to just spray stuff down the drain. The grid was just in the way.

Our came with grids, so we are trying it out. Yes, I do like that things don't sit on the sink bottom and there is a little cushion and water can move freely along the bottom, but I don't think I would have paid extra for them. I don't like that food gets caught in them, but I do have a sprayer, which helps. I may have a different opinion in 6 months - I may really appreciate the grids then.

for about $7 you can get an Ikea trivet and see if it works for you.
The steel cross bars are too widely spaced to be a great sink grid, but it works.
I bought one.

LÃMPLIG Trivet $6.99

I have one in my D shaped sink and love it. I can't remember if we paid any extra for it, 1 granite place had it as a throw in, one did not. I would pay extra for it.

the not blocking the drain and keeping things nice and level and away from the bottom is huge for me. I do have a sprayer and wash any gunk with that but not an issue really, and cleaning the sink I only do once every week.

I ordered my sink (not installed yet) thru galaxytoolsupply.com and the price included the grids. I currently have a white cast composite of some sort (don't really know the material) and grids would've been nice with it to prevent the scratching. So, never used them (yet) but think I will love them, tho I don't know if I'd pay extra for them. Definitely not $240!!

The grid is not a necessity but I am glad I got one for my silgranit sink. It's not that big of a deal to lift it up and wipe down the sink at the end of the day. I have a great faucet with strong spray action so no food gets stuck in the grid. It protects the sink and just looks nice.

While I wash everything in the DW, I do love the grid - although I didn't initially want one. DH talked me into ordering it, and have loved it ever since: it's so useful to be able to leave a colander draining, yet be able to run the tap, over on the other side to rinse something, or wash my hands, without swamping the colander contents.
I was really surprised at how much I like it - and cleaning is simple: just put the plug in the sink, fill with enough soapy water to cover the grid, swish it over with a brush, and it's done. Or you can put in your DW.

thank you so much for the responses. for the moment, we're going nekked. if we change our mind, i'll opt for an after-market grid as we are now officially spending way too much money!