If you are doing any business or marketing on Instagram, then at some point, you have been annoyed that you can only put one link on your profile. For a lot of users and most photographers, the ultimate goal is to drive traffic from Instagram to your website/portfolio.
So, it makes sense that most of us put our website as that one link. The problem arises when you have something timely or new you also want to promote. Maybe you have a project you are pushing or a new blog post. Perhaps you're selling products like prints or books. You could just be trying to get more subscribers for your newsletter.