It isn't that big of waste of time, the build plate can take up to 8 minutes or so to fully heat and the hotend takes about 1-2 minutes. If you are doing hour to 2 hour or longer prints that is a small fraction of the time of the total print process. I can see it being a big time waster if all of your prints are 30 minutes, but then you need to think about putting more on the build plate at one time to maximize your make ready time efforts.
For ABS here is my workflow.
Preheat bed to 80c, this takes about 4 minutes max. I've never timed it.
Bed continues to heat to 95c, takes just a minute or so.
Hot end heats, 2 minutes or so.
A lot of times I will be finalizing my prep in S3d while the printer preheats.
You also really don't want your filament sitting there cooking for 6-8 minutes while the build plate is heating. The best scenario is the hot end heats and as soon as up to temp it purges, skirts, and prints.