What's the difference between Tactical Might and Siege Might?

Siege might gives bonus might only when you are attacking a castle (not when you are under attack, nor when you attack reinforced tiles in roc/eden). This bonus apply to both troops attacks and skills damage.

Tactical might will apply in any battle, but it will only affect skills damage.

If you are attacking buildings (bridges, gates or towns) in eden, siege might won't be effective, so tactical might is better.

Non siege might