While there’s a few instances where it’s worthy, it’s mostly not worth it. There’s some benefits to purchasing multiple domain names and forwarding them to your primary domain name, but none these reasons are not related to SEO.
“Buying up secondary domain names and forwarding them to your primary domain is a good way to protect your brand, catch typos and be memorable. If you’re only doing it to attract search engines, I recommend saving your money and spending some time writing unique, quality content that’s relevant to the users on your website.” ª
Protecting your brand.
You could choose to register a secondary domain and forward them to your primary domain which might be “yourname.net set up to automatically forward to “yourname.com”
If there’s variations on your brand name or locations, getting other domain names would also make sense, so that no matter which location someone types in the url bar, it’s forwarded to your one main website (ex: yourname-commons.com or yourname-treecity.com all forwarded to yourname.com)
If you had to just pick two, get your primary domain and a country-based domain also, especially if your brand is your specific name. For example, a Realtor named Michael Smith might want to have michaelsmith.com as his primary domain and michaelsmith.us as his secondary.
Your domain name might have a common typo.
If your name has more than one common spelling, you might want to buy the domain you seek – spelled both ways. For example, lolli-pop can be also be spelled lolly-pop, so you might want to buy: brightonlollipopshop.com and brightonlollypopshop.com
ª Quoted from The Dojo, 1/22/16, originally written 10/9/13 by