I always pack light. It allows me to go fast. I usually carry one pack. And I never check luggage. However, often I also need to carry with me things as I am on the go, either going to and from a meeting with a customer, walking around a target and collecting info, etc.
In these cases, there are many things to do. I can use the same pack, leave all the stuff at the hotel or apartment, and carry stuff in there, tough this is rather bad, since the main pack usually is bigger than needed. So, what I like to do is carry a smaller pack inside the main pack (in this case a GORUCK Bullet 10 inside a GORUCK GR2), and as soon as I get to the location, stash the main pack and move light and fast with the smaller pack.