I think the FROM field in the form overrides what's in the SMTP settings, but it's still a good idea to change it in SMTP because it will be used to send email outside of Gravity Forms.
For example, I have "My Company Name" in the settings, but in the forms, I have it set to be sent from {Name:1} because I want it to appear it's coming from the person filling out the form. In the From Email field, I have "sales@mycompany.com" (which matches what I'm using in the SMTP settings).
When someone submits a form, it works great.
Since I'm a new user of this plugin and want to make sure everything is working properly, I also installed a plugin that sends a periodic report of form submissions just so I can double check. When I get emails from that plugin, they show up as coming from "My Company Name".
So that would be an example of when that field is used. Hope that makes sense!