Ok, I'll give this a go...

High value depends on the dog and what they like. Things that they totally love are high value treats, things they can take or leave or just normal value treats... It can also depend on the location and circumstances as to what a dog considers high value... Many treats that they love indoors and go crazy for, they can barely get enthusiastic about in for example a training class or in the park!
Here's when you would normally use high value treats as opposed to normal stuff:
1. When teaching a new exercise
2. When practicing an exercise in a new location
3. When practicing an exercise with more distractions
Indoors, I sometimes use high value treats, particularly when teaching new exericses or if I need the dogs to respond quicker and better and more enthusiastically. However, I often use just every day kibble indoors as this is normally enough.
Outdoors I always use high value treats when doing things, the distractions are too much - particularly for my lurchers which are distrated very easily.
In training classes, I always use high value treats as we are either teaching new stuff and the distraction levels are generally high!
Hope this helps.
Vera