I've been in homecare for about 11 years now. I have always used a shoulder bag until I started at my recent job where they offered me a bag on wheels because I was having shoulder pain from the heaviness of the bag.
I agree with the last two posts that bag barriers are to keep your patient's home clean and to keep you from dragging something from one house to the next.
I, too questioned how I could use the bag on wheels and still keep a clean bag. I opted against it.
Instead I got a shoulder bag and then spent $20.00 at Target to buy one of those folding grocery carts.
Now I can pull my bag without having it touch the ground or the floor of the patient's house.
The other problem with the rolling bag is that you shouldn't put it up on a chair or table to get into it, which means a lot of deep knee bends during your day!
Hope this helps.