Well, not specifically because I want to make them feel included, it is to stimulate them and satisfy their curiosity. Also helps skittish cats and dogs to gain confidence by introducing them to new smells constantly in a safe way.
Smells are way more important to both cats and dogs than humans, and more than most people realize. Example: I see a lot of people around walk their dogs and not letting them sniff properly but just tug them along, thinking that the physical exercise and waste management are the sole purpose of walks.
We have a retired hunting dog, turned 11 on Sunday actually, and she's still ridiculously hard to tire by physical exercise. The only way to get her proper tired is mental stimulation. Sniffing is a big part of that. 30min calm patient walk is way better than 60min of "COME OON" -hurried impatient walk.
Disclaimer: not all dogs etc., but... most dogs.