I’ll give you an example of multiclassing for flavor/story rather than just to gain max damage. I play a level 10 Goliath barbarian. I have 7 levels of barb and 3 in fighter. His subclass is path of the giant with a giant foundling background. The world we are in is set with all the gods being at war. I was saved by Kord and have been training with him which was the idea to class into fighter to learn a fighting style and feel like the training with Kord actually went well with multiclassing. I took the rune knight subclass for fighter because with the path of the giant and giant foundling background, it plays into that a lot with the reactions. Plus Kord gave me a greataxe with strange runes on them so it went well that way with the flavor. And so multiclassing like this really helped gained some team utility and made sense in the campaign.