Pretty much all the time. Whenever my cat is staring at me and I have something in my hands, if he's close enough to sniff, I hold it where he can sniff. Doesn't matter what it is.
If it's food, and maybe the food is something he is interested in, I can see his expression/posture change, and I pull back and and separate a small, cat-sized bite for him to try, being careful to only give him cat friendly morsels, like a piece of meat or something.
Usually he doesn't have any interest in what I'm eating, so that's rare. Most of the time he sniffs, then retreats to a safe distance, uninterested in what I'm having... I just think he's not sure until he gets a good whiff; so I give him one.
One of mine would pick up mini marshmallows with a claw, lick all the powdered sugar off and then shake her paw to get rid of it, flinging the wet, sticky blob off into the unknown.