You left out the nearby sentence that includes the word "potentially" as in
"This potentially can cause more data storage to be used"
The pointer argument still holds, protecting you from massive duplication of 3rd-party DLLs when you branch. But if you CHANGE lots of these files in one branch, then it must try to find a way to keep up with the differences.
I recommend Bill Heys' post on the subject
Unless you do some really weird things with your dependencies, I don't see you will have a problem. First, a sensible strategy for dependencies is to put them in folders with version numbers on them. So you would usually not change a file, but would simply add a new version from time to time. In my experience, we do not churn dependencies a great deal.
If you are still nervous after reading Bill's very authoritative (from the product team) post, just do a quick experiment and watch your database after adding 100 MB of DLLS and then branching.