Usually you can just use it as an abstraction layer kind of number. Once you get a GV number you can tie in your other endpoints like cell phone or home phone (or both) to have the google voice number ring those devices. If you no longer want to receive calls on that number, you can disassociate your 'real' numbers such as your cell so people can't call it using the google voice number.
If you disassociated your original mobile phone number from the GV number, what is the purpose of having GV?
So on that end it's useful for temporary transactions such as Craigslist.
I use CL occasionally. I really don't like giving out my number, but it seems people respond via email a lot less these days versus mobile. So in this instance, would I give them my GV number or mobile number? I'm trying to figure out which one is more secure.
I believe the second part you are referring to is where you can port your number over to GV to have your main/normal number instead become your google voice number. You'd still need a number for your remote device such as a cell phone so you would have to get another one from the provider. Most providers cancel your contract or account once you port the number away from them.
This was one of the things I could never understand until I read your explanation several times

I guess the video makes it seem like GV is responsible for you needing to get a new contract from your provider. I guess since they're porting your number, the provider contract getting cancelled is inevitable.
But I just don't understand what you would do with the new mobile phone number that your provider would give you. Is this number useless? Does only GV need to know what this number is? Can this number be given out as a new number to friends, family, and co-workers? Or would that defeat the purpose?
I believe the number port is only optional and you have to manually specify if you want to port it over. For most people you would just hand out your new google voice number instead of having the hassle to move everything around. The main advantage to porting is that you retain the same number you've always had but then can associate it with other devices or numbers as forwarding points. Then if you ever change cell service or similar you can just adjust where google voice points to, but people would still call your same number they've always known you at.
So, I would have zero use for a GV number if I ported my original mobile number?
So basically what they're saying is you can port your current number over to Google Voice so you can use that number with the service and not worry about giving people a new number. You would end up getting a new cell number from your carrier so you can receive calls on your phone forwarded by Google Voice.
So, the new cell number from the carrier, after porting, only has use for Google Voice? I wouldn't even use it?
I migrated over to my Google Voice number, I didn't port it as when you port a number you cancel your contract.
My preferred method is just to give people my new number. Since I still had my old, it wasn't a big deal to tell people my new number, and this way I can easily switch phones or cancel my plan without having to worry about getting my new number out to people ASAP.
If you use the GV number that they give you, what do you do with your your provider contracted mobile phone number? What is the purpose of having two (or more: other mobiles, work, landline, etc.) phone numbers?
What I love about Google Voice and Hangouts is the ability to call/text from any phone, just install the app and sign in, and you can call/text over WiFi as well.
I don't understand this either. People can still call/text from any of their phones without Google Voice. How does GV help with that more?
I'm just trying to wrap my head around all of this. It seems like a really cool feature (Google Voice) and yet I don't understand it.