Hi all,
I think it is helpful to practice keeping a constant "pace" when working on your chops by whatever means which suit your individual preference, BUT, not much nicely composed music does actually has a constant beat at all!
This keeping the same "stride" kind of a thing came to furore in the worst time frame (IMHO) in our modern music, The Disco.
Also because a lot of the music is now produced on a "single" based time frame (maybe 3 to 4 minutes max.), it is not easy to have tempo variations in such a relative short span of time.
It is an absolute eye-opener to check the "pulse" on well known music and find out how much it varies!
One of the charms of improvised music, like some Jazz but particularly the gypsy inspired Eastern European (slavic, think violin, Django Rheinhardt) is the sweeping build-up to a point of crescendo, which can enhance the musical experience (from the listeners ,audience, point of view) greatly.
Even when the tempi variations would be very slight it still can have a great bearing on the "feel"of the music.
Cheers and happy drumming,
Harry