It depends on the product - few people seeing lucidchart in their facebook feed have any use for it (or at least don't recognize said use). Lucidchart is a product where you only need it under fairly special circumstances (small niche).

The case for Pepsi is completely different - anyone can drink it, and just about everyone already knows about it, so social media is largely brand marketing.

I'd like to see comparative analysis of different social media campaigns broken down by what the existing ad spend is intended for, and also broken down by the main pre-campaign marketing channels.