I've not heard about yellow tags, but.... We are going a week Monday and intend to use the Disney Collect our bag service for the first time. It was hard work previously trekking luggage all the way through the airport so we didn't have to wait for a second carousel as that had previously taken ages! We only had one young child last time and this time we have two, so it's a no brainer!
We have planned to put in hand luggage though, a spare set of clothes and pyjamas and small toiletries for when we arrive at Disney as the others have said it could take up to 4 hours for clothes to arrive.
I can always update after my experience if you not going within the next week?