Android/iOS: One of the best little features in Waze is the ability to share your location and ETA with a contact. This way, you can answer the "when will you get here?" question before it's even asked. Now, you can do that in Google Maps too.
To share your location with a contact open up the side menu, then tap Share Location. Tap a contact, and you'll see different options for sharing. You can choose to share your location from 15 minutes or up to three days. Alternately, you can share your location all the time until you manually turn it off. You can tap that same menu to turn off sharing at any point.
More useful is sharing your ETA on a trip. To do this, start navigation, then tap the More button at the bottom of the screen. Tap Share Trip and select the friends you want to send your ETA to. You'll stop sharing your location the second you arrive at your destination. As always, Google's rolling this feature out gradually, so keep an eye on your Google Maps app on Android and iOS over the next week or so.