A CMS lets you edit your website without touching code. That is valuable if you publish articles, change prices or add products regularly. It is much less valuable if your site changes twice a year.
Every CMS adds something to look after: updates, security patches, plugins and a login that needs protecting. For a small brochure site, a well-built static site is faster, cheaper to host and has far fewer things that can break.
The question to ask is how often you will make changes and who will make them. If the answer is weekly and you, a CMS earns its place. If the answer is rarely, or I can do it for you through a monthly plan, you may be better without one.