You can deduct a *lot* from tracking a user these days. Especially with all the data smartphone apps offer up to their suppliers. You basically have a more complete and trustworthy personal profile of a person than the person could probably even willingly give themselves. Sleeping habits, areas of interest, modes of transport, typing speed, wording/education, interests, income, temper, sexual preferences, political affiliation, religious beliefs
Having a large set of algorithms chose your partner for you based on such data is most likely to be a better choice than most humans could ever hope to make. The computer already knows much more about both mates than each could know about each other in years. And bring people together who would've never come together under regular circumstances.
Finding a fitting mate would actually be one of the better reasons for me to offer my data up to some app.
My 2 cents.