Functional Obedience - Yes
With this simple command you can take a snapshot in time and mark that behaviour that occurred during that snapshot as the correct behaviour. This allows you some time to reinforce that behaviour.
In order for "Yes" to work you must first teach its meaning to the dog. Have the dog near you - within arms reach - say "Yes" and then offer the dog something that they like. Moist food is good to use as it can be delivered quickly, in rapid succession and can be consumed quickly. Importantly though is that the dog must love what is being given.
Repeat this process five times and then give the dog a break. Repeat that set 5 times per day for 2 days. Some dogs may need longer, some less.
Notice the reaction of your dog between repetitions and most importantly between sets. You will notice at first a slight interest which then rapidly moves to motivated engagement with you. Then you break the set off and allow the dog to mull what just happened over.
When you come back to it, the dog will start a little better and finish much stronger.
Do not become too keen to break of the conditioning process early, continue for a couple of days and then you can reliably use the "Yes" signal to indicate to your dog that their current behaviour is desired and that that completed behaviour will be rewarded.
What we have done is create a bridge between time. The instant the dog does what you want you say you can now communicate instantly, then you have a time to reward your dog and reinforce the behaviour. This comes in handy when you are teaching skills to your dog from a distance, such as a Stay with you out of sight.