First of all, I think this is a conspiracy. Every fucking time I post, I swear it's like, "This post is doing 90% better". 90% better is a lot better, and I see it way too often. That is one thing. If you have a business account, Instagram is trying to sell you advertising, obviously, and get you to pay to promote your posts, so when a post is doing well, it will say, "Hey, this post is doing 90% better than your usual posts. Do you want to promote it?" The idea being people are already resonating with this.
Do you want to pay to make sure more people see it? You know the amount of people that are seeing an Instagram post are between 15% and 50%-- really between like 2% and 90%. I would say the solid average is probably between 15% and 40%, so you can pay to maybe have 60% of your audience see it or to have people who aren't part of your audience see it.
Should influencers be paying to promote their feed? I don't think that that's super valuable. I don't think it's a sustainable way to grow an audience. I think that the chances of somebody looking at your post, clicking to your profile and following you off of a promoted post that you've done are essentially zero. I would not promote it unless there's a business reason to do so outside of gaining a following. If you have a message that you're trying to get across, if, obviously, you're working with a brand and they want you to promote it, that's the time you would do that obviously.
Let's say you're launching a new clothing line or a collaboration with a jewelry brand and you want as many people as humanly possible to see it, I would put some money behind that. Don't listen to Instagram and put money behind posts just because they're doing well. If you're going to pay to promote your posts, make sure there's a reason other than "I want to gain followers" because I don't think that will work.
- Influencer Marketing in 2019, Instagram Story Content, Boosting