I believe MWD refers to gathering intel (may not her exact words). What I feel becomes unhealthy is how it seems almost addictive to the LBS. I have seen some that was haunted by the information they gathered, and yet, they would continue going back to read through emails and text messages. They got more caught up in snooping than in working on themselves. The information they received through snooping affects some people after the M is reconciled, just as some LBS's cannot deal with knowing every little detail of the AP's having sex. (However, MWD says they should have all their questions about the affair answered). The LBS is stuck with those images branded in the mind. Each person has to decide what is healthy or unhealthy for themselves. I just know there have been so many who have said they wished they had never known.
These "rules" are just a guideline to give newcomers a place to start DBing. I will just say that each person has to follow their own conscious and do what they feel is right about #10.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!