It is another point of failure. I'd hope that this point has a lower frequency of failure than otherwise.
Consider:
Adding one line of code to a page and then adding 5 scripts added from a vendor-approved and tested library.
Adding 5 snippets of code to your own site in various sections on various pages.
Because you would be putting some everywhere, some on specific pages and some only firing on special rules, you actually have a lot that you have to manage. You could just put this in your CMS or in some version control, but then they aren't all in one place anymore, but scattered all over your code. If you want to remove something, do you just remove it in one place or everywhere? If you need to make a change are you sure you have done it in all the right places? If you need to just pause something right away, how do you do that, without changing your live site?
All these things require changes which have a higher likelihood of failing, than doing it through a properly controlled automated system.
