1) Brand SEM terms are cheap - if you own the brand, especially something like Squarespace, your ad will have a high quality score and will thus pay a much lower CPC than a competitor trying to vie for eyeballs with your brand name as a keyword. This means that brand terms generally are pretty cheap to buy.
2) Real estate ownership - The more real estate on the page you own the more click share you will get. This will keep other organic listings from getting click share which may mean your competitors will get less traffic off of searches for you.
3) Control over message - Ads provide a high degree of creative control which means you can change the copy and also add on Ad Extensions like sitelinks, app download buttons, "click to call" buttons, etc. These are all things that are harder to control on your organic listing.