Whatever they need. Alphabet Inc. is made up of a dozen companies with thousands of products. There's always something that can benefit from such insight.

The location data that Google collects through Android phones, alone, is mind-blowing. Just from your daily movement they can figure out where you live, where you work, shop, eat, drink, vacation. Indirectly they can figure out who your friends and relatives are, your partners, extra interests and hobbies etc. They sell all that to advertisers, there's a reason why so much of Alphabet revenue comes from ads. Then there's more complex patterns like traffic for example that they can sell to city planners and so on. And that's just location data.