DH, I and Uni aged daughter have it for practical reasons, Uni aged son prefers not to have it - up to him.
When DH is on the train coming home from work, I can check his ETA so that I can time dinner accordingly without having to ring to ask his ETA.
When DD comes back from a late shift (1-2 am), I can just check that she's back safely in the night without having to get out of bed and look out the window to make sure her car is there.
When we're at the supermarket and DD wakes up, she can send messages like " can you grab me a deodorant/a watermelon" or whatever she's decided she needed.
When DD drives back to Uni, we can see she's arrived safely without her having to call us. DS has to ring us (or us ring him if he forgets).
If anyone is picking anyone up from the station/airport etc, we can keep on top of arrival times without multiple calls/texts.
If we're caught in traffic, we don't need to stop to make a phone call or send a text.
Basically it's a useful tool. Why would be so worried about sharing where we are with each other. In this house no one is controlling and no one is doing anything they need to hide - so there's no reason not to make our lives easier with a tool that gives us information. Similarly, we're absolutely fine with DS opting out - but it does make his life harder and mean he has to make more texts and phone calls, and probably wait around more for us to arrive places as we don't have that real time information. I can see that it could be misused in cases of control, but honestly if you're living with a controlling partner, your phone app is the least of your problems!