Here are two ways I use GV:
I still have not switched to having most people call my GV number due to initial reliability problems with some people not being able to get my GC number to ringg.
The other day I forgetfully left my ATT cellphone home when I was expecting an important call to that number. Fortunately ATT customer service can still establish call forwarding if you call them, but they are changing systems and soon will no longer be able to do this. So they arranged all calls to be forwarded to my Sprint phone which I did have with me.
For the future when you can only establish call forwarding if you have your phone physically with you and aTT customer service can not do it, I set up another Google Voice account. (My first GV account forwarded calls from my GV number to all my cell phones. The new GV account will forward unanswered calls to my cell phone on to my home and work phone and my second GV number which in turn will forward it to any cell phone i have with me.
Sprint used to charge for all call forwarding but I read that since last November they no longer charge for conditional call forwarding (that is only forwarding if the number is busy or unanswered or both - (*73, *74, *38)) They still charge ($0.20/minute) for unconditional call forwarding (*72).
ATT only charges minutes plus
long distance fees for any call forwarding.
This arrangement is actually better than what I was originally contemplating as it is automatic and many of my missed cell phone calls happen when I am at home and not carrying my cell phone with me and don't hear it as I am in a distant part of the house or outside. My ATT DECT landline wireless phone system did have an option to pick up phone calls to one of my cell
phones and relay to the land line system, but it kept loosing bluetooth pairing so it was unreliable. So this new arrangement will ring all my house landline phones if either cell phone is called and not answered.
The other way I use GV has been touched upon. I use it to take notes, make lists, and keep records by calling and leaving a voicemail which it then transcribes. This is handier than using a voice recorder for information that needs to be transcribed.