If we speak professional language, visual identity is part of branding and I provide services specifically for those companies and bloggers, who want to promote their skills/products in Instagram as it's one of most popular platforms with its own specific details. However, the main ideas that we create as concept base you can also use for all design materials for your brand.
So, If you don't understand how to translate & show audience your brand mission and TOV, how to show expertise in your account and retain your personality, how to shoot your products in favorable angles, how to visually highlight a specific product line in your Instagram feed, what to shoot in general and in what format/quantity, how to achieve your unique style, what color scheme choose and how it'll fit your theme - visual identity answers all these questions.