Cfxtrjtrk

While defining an environment <env> also defines the <env> and end<env> declarations, what are the circumstances where defining those declarations directly (without defining an environment) is preferable?

I see the following use where proof and endproof are defined separately in the informs3 document class file:

%% Use for proper proofs that end with extra space (regardless of the use

%% or non-use of qed (=the black box)

defproof#1{Trivlistitem[hspace*{1em}hskiplabelsep{it #1enskip }]ignorespaces}

defendproof{endTrivlistaddvspace{0pt}}

Is there any reason not to do newenvironment{proof}[1]{...}{...} instead?

newenvironment other than checking that the name is "safe" to define does nothing different to the def forms that you show (apart from using longdef unless the * form is used).

Especially in older code you will often see the lower level form, going back to when it could take several minutes to load a style file and not doing the checks in often used but unchanging definitions was a useful saving.