Use
[url] when certain characters would trip up the code. Remember i=t because you'll need
[url] to fix spaces in urls. But anywhere a &, $, !=, space, etc could be a problem: commonly, all search/append/replace/delete t=ags (&), showif/hideif (!), urls. Note that you don't have to waste your= time url'ing every damn value written to a db. If you control the value and= know it's clean, like a T or F or a number or word from a value list, no ne=ed. When a user inputs or you pull something like company names from a db, t=hat's when you need it.
[input] is used when quote marks and returns w=ill trip things up. Values within <input> tags and in java scripts. No=t just in <text area> but also in all other <input> tags, i.e., v=alue=3D"
[input][whatever][/input]" -- same idea about js.