What is the idea behind this (I mean taking 5 to 8 practice tests)? Do they serve as milestones to track the progress or just as means to get used to taking long tests?
Both. Your goal is to maximize value derived from the practice test (benchmarking and assessment for moving forward).
It would be useful if people could indicate their final GMAT score and the number of practice tests taken during preparation.
You need to go through the debriefs in the share your GMAT experience forum for this information.
Strategy Discussion Thread | Strategy Master | GMAT Debrief| Please discuss strategies in discussion thread. Master thread will be updated accordingly. | GC Member Write Ups