Edit: If you dial a number by clicking a link and then answering from the Gmail page, the number 4 on your keypad will appear dead. On incoming calls the 4 is used to turn on recording the call. To have the 4 work in normal fashion you must initiate the call through the chat phone link on the Gmail page.
I use Google Voice more and more. Cell service in my winter home is miserable so for my calling out, Google Voice is the answer. The Gmail dialer is primitive and limited but interfaces with Google Contacts nicely. Now we no longer have to cut and paste phone numbers that are not in our contacts. Left click a phone number on a web page or email and Google's dialer pops up with the number entered. This is a welcome enhancement.
My non-geek friends don't use Google Voice for some reason. They have no motivation to set up a phone number. They are missing out on a great function. Why search a location, find the number and use a phone? Just left click and call free.
Things you need.
Google Voice has sophisticated functions within it's settings for handling calls and messages and I use some of them but this computer as phone functionality would be enough reason to have a GV number even if it did nothing else.