My query arises from my answer to Tab not as extra alignment tab and Andrey's rather nicer version. The question at hand involved making the TAB character usable for aligning tables. I assigned it to catcode 4, alignment, whereas Andrey used catcode 13, active characters, and then
gdef'd it to
So my general question is: supposing we want to make a new character act like
^ or whatever, when is it best to reassign a character to a more specific catcode (like 1-4, 7, or 8), and when is it best to use the all-purpose catcode 13?
(In the related question Active characters let to a (non-active) character it was mentioned that it may not be a good idea to redefine existing characters in these categories to active versions of themselves, but I'm talking here about making new characters.)