The problem with blocking trackers and so forth is that it normally causes slowdowns.

This is visible if you use for example Ublock (any privacy filter or any multipurpose filter) you will encounter slowdowns on sites such as groupon and have no ideal why?

It's because they function like black and white and though this is good for you privacy, it's a nightmare for performance. The reason is some sites refuse to finish loading content until they have planted theirs seeds or cookies. What ghostery does is nagivate this landscape for you and decide which seeds are good and which are toxic, dispose of the bad ones, keep the good ones so the site can load without "Access Denied" lag that you get for privacy filters which literally keep the site from loading sometimes for upwards of 10 seconds.

Any user serious about browser performance should disable any privacy list and multipurpose list in their adblock addon and use Ghostery instead.