Profiling is looking at the real data to find out what is actually in it. It takes a day or two and it is the only stage whose output tells you whether your timeline is honest. This article gives you the seven checks to run on every extract and what each one changes.
The short version. Run the same seven checks on every table before you map anything, and turn each finding into either a rule, a scope decision, or a risk on the plan.
Why this is its own stage
What do you think the difference is between profiling and cleaning? Answer before reading on.
Profiling finds out what is there. Cleaning does something about it. They get merged in a lot of write-ups, and merging them costs you the moment where the findings could still change the plan. Once you are cleaning, you have already committed to an approach.
