.com.co is for local (Colombian) end users.
Until recently it was not possible to register under .co directly, many other countries still use domain names at the third level eg. .com.au .co.uk.
The registry promotes .co for international (global) use and .com.co for use within Colombia.
Do you need the .com.co of your .co, probably not unless you do business in Colombia or it's just another defensive registration. But if you own a .co you presumably don't own any other major extensions like .com .net or .org. So you probably won't bother.