Is there any reason to build a higher tier fort than 1?

[Wizzington]

Up-to-date fully maintained forts will give you army tradition in 1.13 (scaled depending on how many forts you have compared to your total development).

 

[Dnote]

I use high level forts on key strategic provinces, some within my country, but mainly in my over-seas provinces where I don't keep large standing armies.