Just as important as knowing who your audience(s) is/are is knowing where they are. These days, you have to look at social and which platform is right for you based on where the bulk of your audience is going to be. If you're doing B2B sales, then LinkedIn must be included in your marketing. If you are B2C, then Facebook, Instagram and even TikTok and Snapchat can be good platforms for you.
Your market research should reveal where you should expect to see the best results for your marketing dollar. Why waste money on platforms and campaigns that won't deliver for you because your audience just isn't there.