The "isolation" drills, like the pad work, is just another way of drilling the fundamentals, in a freer environment.
Chi sau, develops frame, personal alignment, aim, dynamic sitting, two live sides, basic power development, sensitivity. Laap sau, develops entry lines, side/back&forth movement, adjusting lines to entry attacks (challenging gates), bong/wu hitting, etc...another step closer to free sparring. Pads bring about a further development of timing, hitting a moving target, non contacted reaction to movement, checking positions, some conditioning too, etc..
Not necessarily vs specific techniques, but I do brings forth certain ideas of cutting in on someone's attack, utilizing our forward wedging triangle to dominate that center area while coming in or when retreating.
To really utilize the skill set above, the person may choose to take it all out for a test drive vs other ppl/styles/systems just to get a sense of different timings, distance control and one's ability to read different opponents, whenever some weakness comes up, whatever it is we work it in the VT drills, unless it has something to do with non contacted reaction to something happening, like the opponent is just being too fast in their striking or takedowns..
IMO and experience
J