I am not sure that I quite understand the question.

With the modern rig,  and your boat is young enough to come into this category,  you will normally find that when no sails are set but the shrouds are correctly adjusted it will require a modest amount of force to physically push the mast forwards so that the gate can be closed.   Thus there will always be some load on the gate when no sails are set.

With sails set and drawing that situation may change,  depending on all the conditions;  wind strength,  rig tension,  kicker tension,  etc.   In some circumstances the load on the gate may then vanish,  and some keen racers use wedges to better control the position of the mast in its slot.

Does that answer your question?

Oliver

If the boat is left with the mast stepped I personally would always leave the mast gate closed.

I suspect that if you feel the boat is not sailing as previously I think the cause is more likely to be something else,   unless of course the difference is only imagined.

Oliver