Sheets of paper with loads of lines; each size is indicated by a certain-type line and you can only carefully and accurately follow it.
What happens when you buy a multi-size pdf-pattern? - Your printer has to produce many extras you do not need... All sizes would be printed together, and you would have to carefully select, mark and cut your own size out.
PDF Layer is a feature which allows some content to be made visible or invisible in the PDF.
MC2-Patterns started developing LAYERED PDF-PATTERNS.
It means that in our latest patterns each size is on a different layer and you can make visible/printable only the size you need. You can also print, let's say, two sizes when you want to implement changes by emerging them into one pattern making it fits you.
Look for this icon in the navigation panel of Adobe Reader when you opened your file. Click on that symbol and close unneeded layers/sizes.
Why bother, you might be asking? Of course, you can still print all of the sizes like before (pattern pieces are still nested). But you might find it handy to print fewer sizes at a time because the markings on nested patterns can get a bit hard to discern, especially on small pattern pieces.
Perhaps, this is not a big deal for you, but why let such a waste of ink and your time?