Automations are actions carried out by timed intervals. The difference between actions and triggers is that triggers executes its' actions when creating, updating, and removing things.
Let's say you want all companies that have a certain marketing score, and number of employees or revenue be assigned to a role. Simply tell the automation to look whenever a company is updated with the minimum marketing score you have set, and check if the revenue and number of employees fields has the right value. If so, assign them to the role. You can also add other actions such as creating activities for the assigned users with the company or sending an email to the user telling them that the company has reached the level of marketing score.
Instead of relying on a user to do this manually, the automation automatically takes care of it which enables the user to focus on other tasks.
The jobs that performs an automation runs approximately every 2,5 hours.