When more context is needed or you need to tie certain traffic directly to a specific campaign, you should use UTM/Tracking URLs.
Tracking URLs are recommended when creating PPC or social media advertisements, publishing on external websites, adding URLs to print materials, and more. If you want to know the specific asset that was clicked, where it was clicked, and what campaign it relates to, tracking URLs are your answer.
For example, if you are purchasing a banner ad on a website, you might use a UTM/Tracking URL to add the name of the company you're advertising with and where the banner will be placed on their site. If you decide to purchase more ad space from them in the future, you would create a new UTM/Tracking URL.
If you purchase PPC ads, you might use a UTM/Tracking URL as the ad's destination URL so that you can add certain details to your reporting, like which campaign the ad is a part of, what the main keyword for the ad is, etc.
And one more example... Let's say you plan to bring a one-sheet to a tradeshow to offer at your booth to potential leads. You might consider adding a UTM/Tracking URL shortcode to the one-sheet so that when one of your leads visits that page, you can tie that traffic back to the tradeshow.