Question regarding supplies in sieges

[Nexus]

So quick question

Currently I'm playing fateweaver and I see a building that says +10 to supplies per turn when under siege

But in battle isn't based on turns

So does that mean like... 10 per turn that the enemy has you under siege and you're units within are taking attrition?

If so... what's the point of that? You'd be better off attacking with the points you got to keep what defence you got stronger.

[Cryten]

Its simply a reflection that while your troops are getting starved, they have more time to build defences. It rarely means anything.

[Elitewrecker PT]

If you attack it's no longer a defensive siege so you can't use your supplies.
So yes, it's just an extra bonus to combat attrition.