Remove internal vents in plasterboard?

I have a 1970's BV house that has vents built into the plasterboard near the ceiling level. This seems to be very common on houses built around and before this era, but not really in new houses.

I am going through the effort of sealing doors and windows to save on enery costs, and I see these vents as being draft creators.

Are there any good reasons not to block these up?

The only one I can think of is that in bedrooms they provide some venting when sleeping in a closed bedroom. But considering that they are not put into new houses, is this really necessary?


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