For me, it was so that when I'm somewhere I don't know, I can type 'home' into the maps search box and get directions.

I turned off Google's activity tracking on iOS a couple of months ago, and only realised that Google Maps wasn't storing my home location when I used it for directions while stuck in traffic and it sent me to a nearby nursing home instead of my house.

I ended up turning activity tracking back on, because Apple maps still isn't fit for purpose where I live (Ireland). I often need directions down small rural roads, and four times out of five Apple Maps won't recognise the destination address, or will send me to a nearby but incorrect location.

mmm, you think they don't already know that?