This seems self explanatory, but it's uses go beyond saving time for students or teachers typing in a URL to join what you are doing. It also automatically creates a QR code with analytics attached to it. This means that you do not have to go to a separate website to create the QR code. You can see how many people have used it to access whatever it is connected to and what type of device they are using.
One Tab is one of my favorite extensions (which is saying a lot) because I seem to find a new use for it at least once a week. I use it most often at conferences to share out my learning and enable anyone looking at it (and me) to review all of the resources I discovered at the conference. Here is an example: http://goo.gl/bK3sFU from #EdCampCNJ this past weekend. As you can see, I had a lot of tabs open, but this way I always have an archive of them to review at later times. I also use it a lot when curating resources for my students. Here is an example: http://goo.gl/SP4RKf. I don't always give them the resources because there is merit in encouraging them to find and evaluate resources, but sometimes I need to save time in the search process. Another reason I use it is to send people resources. For example, we were searching for a new sound system for my classroom and instead of sending 15 links to my principal I One Tabbed those links and then sent him the one link. That way, it saved him time and I knew he was on the right page for each website.
Save to Google Drive allows me to curate resources during Twitter chats or if I am surfing the web with only a few clicks instead of copying and pasting, which doesn't always work. I can then search my Drive later to find the resource, where if I had simply saved the link as a bookmark, I might not remember what it was on the page that I needed.
There are many more apps and extensions I use and they can be found here: https://goo.gl/vjBOfz.