Gmail in its yet another update has made two changes to the highly used Contacts section. Using groups in Gmail Contacts can be highly beneficial specially if you often email few people.
In the Compose section, you can insert all the contacts under a particular group by just typing the name of that group.
Now what Google has added to this feature is the ability to add more contacts to a group directly by just typing the Contact in the “Add to ” dropdown when you are viewing that group. And how you can use it is shown below in the Video.
The second update is that now we can select which “Email Address” is to be used for a Contact under each Group it belongs to. This is possible though only if a contact has 2 or more email addresses associated. I will try to make this clear with the following real example – I have two email addresses, a personal and work related.
Now if you have stored my contact under Two groups say Friends and Co-workers, you can easily select which of my email addresses you want each group to store. The second part in the above video explains this clearly.
Do drop in your comments whether these changes useful for you. I m’ waiting 
Link: Official Source