With VHS versions of workouts of any kind, you perform the workout strictly as produced, in real time; you can create mix-n-matches among VHS tapes, but the time it takes to shift from one tape to another is irritating and interrupts the flow of the session.
The benefit of being able to jump from segment to segment on a DVD is that you have far more options in terms of customizing a particular workout session to your own preferences, rather than doing all of one workout regardless of whether that one workout suits you.
The Timesaver DVD you refer to is Cathe's compilation of segments from the Body Blast series, and have a specific focus. You may enjoy those, OR you may want to create your own compilations. With DVD chaptering, if you feel like repeating a segment, you can quickly get back to the beginning of that segment; you can't do that nearly as efficiently with VHS.
DVD's are also more durable, and are the wave in terms of video exercise technology. And Cathe is The Wave in terms of exercise DVD's, with the extraordinary premixes she creates within each disc.
It's a little tough to describe if you have no experience with DVD's, but all I can tell you is: in December 2002 I offloaded my entire Cathe VHS collection and replaced it with DVD counterparts, and because I can tailor each workout session more efficiently via DVD's, my cardio fitness has improved tremendously. Plus I look forward to the workouts even more because of the "me" pawprint I'm able to put on each session.
A-Jock