When to play shen support?

I'm an engage support main, <Alistar, Leona, Nautilus> and the past few days have been locking Shen every game to practice map awareness and macro things. I really enjoy the champion but as a support I feel like he has some can really tough matchups, he feels a bit like a counterpick champion as far as supports go.

I was wondering if anyone had advice on when to pick Shen support, what matchups is Shen good into specifically and where can he struggle a bit? I have a hard time fighting poke supports and in slower lanes that just want to farm up I feel like I'm not as impactful as I should be but maybe I should just be playing these matchups differently.