I was at a client meeting this week an the question of page download came up so I thought I’d jot down the answer here. TagMan consists of a JavaScript library and short amount of code that is included in each page. The library is standardised and shared across all clients so that users only download it once per session.
To prevent tags from slowing down the page, you can configure TagMan to writes out into an iframe instead of directly into the page. The advantage of writing tags out into an iframe is they will not delay the page from completing like Javascript does. If the business logic dictates that no 3rd party tags need to be served, minimal code is sent back to the page, keeping bandwidth to an absolute minimum and reducing the impact on page download speed. However, if page weight remains an issue you can always store a lightweight configuration in TagMan that you can roll back to in case of an emergency.