Based on analysis of expert opinions and data from digital marketers, the consensus is to avoid using the Engagement or Traffic campaign objectives if your ultimate goal is to generate sales or leads.

While these objectives might seem logical, a lot of data and experience show they can be a waste of money and time if you're not careful.

Why You Should Be Careful with the Engagement Objective
Facebook's ad algorithm is designed to find users who are most likely to perform the specific action you select as your campaign objective.

It Finds the Wrong Audience: When you select the "Engagement" objective, the algorithm optimizes to find people who are "engagers" — those who like, comment, and share. It does not look for people who are "buyers" or "converters."

Poor Quality Clicks: You might get a lot of likes and comments, which can be great for social proof. However, the data shows that people who are most likely to click, like, or share an ad are often not the same people who are most likely to click a link and make a purchase.

No Purchase Intent: As a result, you are spending money to reach an audience with zero purchase intent, making it a poor choice for direct-response marketing.

The Problem with the Traffic Objective
Similarly, the "Traffic" objective is often misleading for businesses looking for conversions.

It Finds "Clickers": The algorithm for the traffic objective is optimized to find people who are most likely to click on a link, regardless of whether they have a history of making a purchase or signing up for a service.

Low-Quality Traffic: This can lead to a high number of clicks on your ad and your website, but a very low conversion rate. Your site might get a lot of visitors who have no real interest in what you're selling.

The "Scientific" Best Practice: Match Your Objective to Your Goal
The core principle behind successful Facebook advertising is to align your campaign objective with your business goal.

If you want to make sales, use the Sales objective. The algorithm will find people who are most likely to buy your product.

If you want to generate leads (e.g., email sign-ups), use the Leads objective. The algorithm will find people who are most likely to fill out your form.

If you want to build a retargeting list, a traffic objective can be used. A common strategy is to use the traffic objective to send people to a piece of content, and then retarget the visitors with a sales objective campaign. This is a more advanced funnel strategy.

In short, while objectives like "Engagement" and "Traffic" have a purpose (primarily for building brand awareness or getting social proof on a post), "science" and data-driven experts overwhelmingly recommend avoiding them if your true goal is to drive sales or conversions.