This is a very common question, and no matter what page you visit there is always a different answer. You can believe this, or that but me being a technical guy, I love to analyze and then figure out really which is the best method to run.
Take for example, a Shopify store with 10 products. Some say it’s best to make 1 campaign, then one adset for each product. Sure it works; but what if you want to scale, what if you want to run tests, what if you want to keep things organized so you know birds eye view which campaign is performing, which needs optimization and so on.