Why collect
"collect only the data needed for a specific purpose and then safely dispose of it afterwards."
I am yet to find a single improvement in a product which is triggered by a research on data from mass snooping but couldn't be identified on general surveys (on streets/questionnaires).
On the other hand, if speaking of wearables, where customer is directly paying for the product, it no longer justifies the companies' arguments of keeping and sharing of data with advertisers for financial viability.