because at the bottom of the current post, will be shown a list of posts that are limited in number to say 5 or 10. If you tag a post "boobs" you could have hundreds (knowing you, thousands but..)
the other method is to use an
article plugin. You can see it in action at my
story site here. You set up a category in the series, then it adds a table of contents. links to all those posts, that are relative. At the end of each post, you can (in your post admin) set which series the post belongs to. It can keep them in order, or you can manually add the order you want.