I think so.

I think it will be really hard to scrub the broiler pan as it sits on the bottom of the sink. (My sink is about 8" deep, and I find that I'm at the end of my "effective reach" when I'm scrubbing something that's sitting flat on the bottom of my sink--I can reach well enough to press hard while I scrub. If my sink were an inch deeper, I'd have to stand on my tiptoes in order to really scrub something)

I'm 5'2", so I don't have the world's longest arms. If I were taller, I'd have longer arms--but then, they'd start so much higher up, which would mean I'd have to bend over more (not just to scrub but also simply to reach in), which would mean it would be harder on my back.

(do you have a "slop sink" or a utility sink or laundry sink in the garage, or do you know someone who does? The top of those tubs is usually 35" from the floor (so a teeny bit lower that the top of your kitchen counter), and they're 13" deep, often. (undermount sinks end up about an inch or more deeper than their own depth, once they're installed)

That's what as 12" sink would feel like to work in--like a utility sink. Of course it would look nicer, but it would feel like that.

I wouldn't like it.

Here is a link that might be useful: utility or laundry sink

It depends on how you use your sink. Many people on this forum have 10" undermounted sinks, making the actual depth about 11 1/2". Both of my sinks are this configuration. I love the depth since they hide a lot of sins. I tend to let handwashables accumulate in the main sink during the day and do one washing around dinner time and things that need to be rinsed before throwing into recycling tend to accumulate in the prep sink for one daily bout of rinsing and transport to the containers in the mudroom. (DH and I both work from home, so stuff does tend to accumulate over the day.) The deep sinks are great for making these things "disappear" from my line of sight--a huge plus that I hadn't considered when purchasing the sinks.

I think if I did a lot of handwashing "in" the sink, the sinks would seem a bit too deep. But my style of washing (with either an 11.5" deep or 7" deep sink) is usually to pick things up out of the water to sponge them and if something needs elbow grease I usually scrub it by resting it on the lip of the sink or on the counter.

My attempt was to make things as flexible as possible in the kitchen and I figured a deeper sink was more flexible than a shallower one, given my way of using it.

Your contractor is right - 7-8" is normal and 10" is deep. You should go to a kitchen display somewhere and try for yourself. I was all set to go for 10" when I checked one out and realized it was way too deep for me. 8" works much better.

Also note tht you can make your 7" or 8" sink seem deeper by getting a high-rise faucetthat gives you good clearance under the spigot, useful for washing big items.

Wow--thanks so much for the great input. I'm also 5'2" so it's good to get an opinion from someone the same height. I will probably go with the 10"--our dishes tend to sit around and we need a hiding place!
Thanks again!

How is your back?
I got the shallowest farm sink I could find. Franke. It is still deep enough to hide dishes. More than deep enough.

keep in mind your countertop height when if you are installing an undermount sink. Your 12" sink could easily end up being a 13" to 14" sink. A mistake my sister made. It was handy but at the same time bothered her to reach so deep. She also has a large family. Large family = lots of dishes.