Earlier this year, Google announced a big change for the Timeline feature in Google Maps, which happens to be one of its best features. While it can currently be accessed via Google Maps on the web as well as through the mobile apps, soon it will be locked to individual phones and tablets (and unless you transfer it over, all your existing data will be wiped).
The deadline for the switch seems to vary between users. Google told TechRadar that people would have "approximately six months"...