I've wondered about this, and decided today that it was worth a discussion.  I assume Token Calculator was originally designed for math functions, but it has moved beyond that.  "Substitute" is a very useful function, for example; I used it today to replace a substring in a series of entry names.  In order to do that, however, I had to manually create a token via a separate "Assign Token Values" activity, set the "For Each Entry -> Current Entry Name" to it, and then reference that token.

Why not just allow me to reference the current entry name token directly within the Token Calculator activity?