Why?

Well, first of all i'm agonizing over character description because I rely on my faceclaims for roleplaying. Second, I am really bad at dialogue between two people because usually I can get away with just writing one person's reactions and speeches. Third, I can't plot for shit. Not the kind that you yell at each other about how amazing it would be if we did..., but actually creating a narrative arc with chapter separations. Fourth, connectivity. With roleplaying, it doesn't matter if time jumps or blacks out. But when you're actually writing a piece, it's hard to do that without misguiding your readers. 

Roleplaying is good if you want to practice your English. It's fun! But you should never just rely on it to get by. You're missing a lot of skills that you need to hone. 

True facts. 

For example, my portrayal of a character changes whenever I switch faceclaims for him. Louis Garrel was more mysterious and broody. Zachary Quinto was more upfront and confrontational. I think it really depended on the gifs available and their demeanour when they act. 

I've seen this in everyone. Loki. Aaron Johnson faceclaim, more trickery and mischievous. Gaspard Ulliel faceclaim, more sinister and cynical. 

Is it bad that faceclaims are so important in RPs? Maybe. But in fandom RPs, faceclaims are part of the fun. You're basically dreamcasting or fancasting. 

When I was stuck with playing T'Challa, I changed the faceclaim around. Instantly, I got his voice back. Because the face was a better fit for the image of the character I have in my head. Does this dampen creativity? I don't think so.