Michael - Thanks for your well put together answer.
Liron - Thanks for your reply example.
Both did help me understand the technical part of this subject.
I still need to understand one more thing I'm finding hard to understand, in the matter of logic understanding - why does Tab 2 is changing its formation after loosely coupling is taking action? how did it became a some what of a "statistics table" (not a QV statistic table) that shows all possibilities of combinations between the variables?
In fact, it works differently in the different QV versions. I used this feature successfully in QV 7.x, where loosely coupled tables were affected by selections in the other tables, but selections in the loosen table didn't affect anything outside it. The functionality was changed in later versions, and in different ways in different versions. I didn't use it since than, and can't tell where it may be needed.
In any case, be very careful about using this option. A good amount of testing is needed to make sure you get what you want.