A common decision when adding a new section or a new project.
USE A SUBDOMAIN WHEN
The content belongs to the same brand: blog.yourdomain.com, shop.yourdomain.com, help.yourdomain.com
You need a staging or development copy You want a customer portal or documentation area You want it to cost nothing extra
Subdomains are free, created in cPanel in a minute, and need no registration.
USE A SEPARATE DOMAIN WHEN
It is a genuinely different business or brand It has a different audience that would not associate it with your main name You may sell or spin it off later It needs its own identity in marketing
WHAT TO KNOW ABOUT SUBDOMAINS
Each needs its own SSL coverage. Run AutoSSL after creating one. They count against your plan's subdomain allowance. They share the hosting account's resources, so a busy subdomain affects the main site. Search engines largely treat a subdomain as related to but distinct from the main domain.
THE PRACTICAL DEFAULT
Use a subdomain unless you have a specific reason not to. It is cheaper, simpler and easier to manage.
