Asking questions is one thing: tag questions are something else, aren't they? I think the idea is a discourse marker . We use tag questions because we make a statement and wish to ellicit a response from someone, don't we? It is interesting to look at when we use a negative tag (isn't it?), and when...

ܐܟܬܘܒ ܣܘܪܝܝܐ, yay!

This is far comfier than the other place!

Gareth.