A couple of reasons - data quality and usage restrictions are the top. Here&#x27;s an example - say I&#x27;m Big Box Retailer &amp; Co and I want to measure how many people who visit my store also visited my competitor, Small Box Retailer Inc. Where can I go to buy that data?<p>-Facebook or Google don&#x27;t sell their raw user data. They can tell me how effective the ads I placed on their sites were at driving visits or sales by matching my customer&#x27;s email &amp; phone numbers to their users (see [1] and [2]), but they won&#x27;t give me data on my competitor, and the data will always be aggregated. So on to the next idea..<p>-Mobile ad server data aggregators might sell me their raw data, but the quality isn&#x27;t great. Sure, they track 100m+ devices...but how many times do they see each of those devices a day? For most devices it&#x27;s 10 times or less, so you&#x27;re going to have a big problem with false negatives (people who visited Big Box Retailer and Small Box Retailer, but due to the sparsity of the data I miss one of those visits). On to the next...<p>-Foursquare is newly in the data business, but despite having a big audience (50m MAU), only ~1.3m users have opted in for continuous measurement ([3]). On top of that, Foursquare&#x27;s audience is pretty skewed - if Big Box Retailer&#x27;s customers are older, I&#x27;m going to have trouble finding them in Foursquare&#x27;s data set, which means the effective size of their 1.3m &#x27;panel&#x27; is really something like 200k-500k. On top of that, I can&#x27;t survey them to verify they actually visited Small Box Retailer instead of the McDonalds next store, since the GPS data Foursquare pulls is LastKnown instead of exact.<p>-...so if the only data I can buy on the open market is skewed, not really that big (not to mention collected under potentially dubious privacy policies), whats my alternative? Thats the need these panels are filling.<p>As an aside, if you&#x27;re curious what apps on your phone are collecting your location data, you can use a self-hosted MITM server w&#x2F; SSL decryption to sniff your own traffic. Here&#x27;s own for Android: <a href="https:&#x2F;&#x2F;code.google.com&#x2F;archive&#x2F;p&#x2F;sandrop&#x2F;" rel="nofollow">https:&#x2F;&#x2F;code.google.com&#x2F;archive&#x2F;p&#x2F;sandrop&#x2F;</a><p>[1] <a href="http:&#x2F;&#x2F;www.wsj.com&#x2F;articles&#x2F;google-touts-mobile-ad-technology-1432220552" rel="nofollow">http:&#x2F;&#x2F;www.wsj.com&#x2F;articles&#x2F;google-touts-mobile-ad-technolog...</a>
[2] <a href="http:&#x2F;&#x2F;www.adweek.com&#x2F;news&#x2F;technology&#x2F;facebook-gives-retailers-new-tool-gauge-sales-154524" rel="nofollow">http:&#x2F;&#x2F;www.adweek.com&#x2F;news&#x2F;technology&#x2F;facebook-gives-retaile...</a>
[3] <a href="http:&#x2F;&#x2F;techcrunch.com&#x2F;2016&#x2F;02&#x2F;22&#x2F;attribution-by-foursquare&#x2F;" rel="nofollow">http:&#x2F;&#x2F;techcrunch.com&#x2F;2016&#x2F;02&#x2F;22&#x2F;attribution-by-foursquare&#x2F;</a>