Often, as humans we easily get excited about the next big thing or idea. Regardless if it's our own or some trending thing we believe we can get into. The response ideally has been to immediately register that domain name, and get all the extra domain extensions too! Don't want anyone to compete with me using dot net! And, it's only about 15 bucks or so at domain registrars! What could go wrong?
Well, 10 years later and you have 8 domains all based on one company or idea name. Such as ExampleCompany.com and then ExampleCompany.net, ExampleCompany.org, .biz, .co, .open, dot everything. It's a bit ridiculous now days with the many, many domain extensions. However, you've now been paying your registrar for domain privacy, protection and anything else they can upsell on each of those domains. So eh, $3 to $4K a year for domain "rentals" isn't terrible for a profitable business. Your burning money. But the question begs, do you really need all of those extra extensions? No. It will not matter if you point EVERY website name registration to your ONE money site you keep maintaining... or don't. Oh, wait, I'm going to have my web person "Duplicate" the main site. Facepalm. You want a great way to NOT HAVE ANY WEBSITES in the search result pages? Yeah, duplicate it all up because Google completely suppresses duplicate content. And for good reason. Google wants to delivery exceptional search results on it's pages, not duplicate content from many different websites.
Having multiple domain registrations is a complete waste of money. But my competitor will buy it and use it. My question is "for what"? Unless the competitor makes a significant effort to invest time and resources (aka Money) into making a new website that will rank in your niche, it's useless. And most times, the competitor will be way more interested in putting their money into their own established website. Not make time to buy domain names of competitors and then try to rank that new site.
In short, having multiple domain extensions for a single domain is not valuable unless there is some real reason other than the ones mentioned above.