Alert By Google: Don't Let Bad Sites On Your Domain Name
If I will give permission to someone to put their site on http://poorsite.semandseo.com/ that would be a not good choice, not just for http://poorsite.semandseo.com, but bad for http://www.semandseo.com.
John Mueller Said:
With regards to other websites hosted within your website, Googlebot doesn't differentiate between accidentally hosting that kind of content within your site and doing it on purpose. If those are really sites that you do not want to be associated with, then I'd recommend making sure that they are not hosted within your domain. If those are sites that you want to fold into your main site, then I'd recommend setting up 301 redirects to the new URLs on your main site.
I just remind you guys, think about it