Note that security essentials lacks central management/reporting features as stated above.It is meant for home use.(not for large enterprises)
Microsoft allows use on up till 10 computers for small businesses.Security essentials should not be used on more than 10 computers,this would imply violating their terms of use
In terms of protection capability,Symantec is much more advanced and stronger antimalware technology compared to Microsoft.
Refer to these testing lab reports:
http://www.av-test.org/certifications
http://www.av-comparatives.org/en/home
(Look for norton antivirus/internet security which use same virus definitions as SEP)