Imagine we use
the same tag for poems and for cooking recipes. Some time
in the future we decide we actually want the mark-up to behave slightly
(or even completely) differently for recipes. This is why we need
separate mark-up for separate purposes.
I would certainly recommend using {{poem}} and {{recipe}} or something
in that case. Then you could simply change the template when they
split.
The parser may decide to close <poem> on the end of the template, so you
can't do it...