Should all subsites look the same?

I am building a website where there is one main site and multiple subsites.

Each subsite targets a different audience trying to accomplish different tasks. Because of that, styling and structure on the subsites vary (e.g. some subsites have side navigation while others do not). However, at the top of each subsite, I do have a global navigation bar that makes it easy to navigate between sites.

Is it considered a bad practice to have subsites that may be drastically different? Or is it okay as long as the changes meet the needs the user is expecting to complete?