Hi,
as a piece of general information:
with respect to models you can imagine the core as a sort of root element for all controls. (and as always, child controls inherit this parent model) Setting a model to the core is like setting one global model.
Doing so is perfectly fine when suitable, but one should be careful: setting another model to the core removes the first one. I have seen people in trouble because they had a sort of tabstrip and each tab initially set its model to the core. When switching forward and then back to the first tab all fields were empty because the second tab replaced the global model.
Regards
Andreas