Lots of times someone I have from one account is also on another account, maybe slightly different information. So if I want to 'call Tom', there could be 5 Toms ... all the same guy, but different information and it could be a pain to sort through them. So this #TipoftheWeek is how to merge those duplicate contacts together into one contact, thus simplifying your "People" app and making it easier to find who you want to contact.
So, right now, without adding in my G+ contacts I have 919 contacts in my phone. That's a lot ... and many are duplicates of each other. I don't want to have to sort through many of the same to find the one with the right phone number or contact info that I want to use.
On Gmail we have a 'find / merge duplicates' option, which scans them all for us.
Handy, but nothing 'en masse' for the phone. We have to find each contact individually... a pain, but look for ones you contact most frequently.
Go into the People app and scroll around until you see someone with multiple entries. Click on any one of them and then choose to 'edit' (I chose the one with a photo... hopefully that means the photo sticks to all of them... sometimes it can be tricky how that works).
In the edit screen you can then choose from the menu to 'join', it'll scan through your contacts and pick what it thinks are potentially appropriate tap one of them and then you'll be brought back to the editing screen and the new information will appear. Repeat as necessary.
You'll notice that when you look through the contact in the editing section that it'll separate the contact info by the account that 'brought it in'.
If you're OCD like me, you like to have clean contact settings... happy hunting!