a page blocked in robots.txt wont be seen at all when a crawler visits your site directly
- Partly true not all robots respect the robots.txt file but Google and Bing do, even if they follow a link from elsewhere.
at times a robots.txt file is mistakenly deleted or moved
- the same can be said about meta data.
That being said the part about "link juice" is a very good and valid argument and reason enough to not block using robots.txt unless you wan't to block an intire directory of images, like the images you use in the design.
In short robots.txt is best used to block non HTML elements like flash, image files, PDF files ex. Where meta blogs are best used to block HTML elements

