xml-dev - DTD conventions/best practice - using an parameter entity referen ceto s

[Dylan Walsh <Dylan.Walsh@Kadius.com>]

I noticed in DTDs that some people will always use an parameter entity
reference, rather than specifying a content model directly i.e.

<!ENTITY % Hr.content "EMPTY" >
<!ELEMENT hr %Hr.content; >

instead of:

<!ELEMENT hr EMPTY >

I can see the advantage of this approach when some or all of the content
model for an element is long and/or is likely to be re-used elsewhere. In
these cases, the parameter entity reference allows you to make a correction
in one place, and save typing. However some people seem to do it everywhere.
It just appears redundant when the text is not going to be re-used, and it
increases the size of the DTD. 

What is the reasoning behind this approach? Does it relate to the using
declarations in multiple DTDs?