To all the apathetic defeatists who won’t delete their search data: your threat model is wrong.
Yes, it sucks that your personal details are already owned and exploited by major corporations. And I agree, aggressively protecting yourself against this may not have the best value trade-off.
But there’s another player who probably doesn’t (yet) own all of your data, but could in a moment: the government. Unlike corporations whose only interest is to sell you products, governments are interested in prosecuting you based on any evidence they can find that you have done anything wrong. The more your data is centralized in one location, the easier it is to sobpoena. If google has your search history, your photos, your email, your calendar, your instant messenger conversations, your documents, and your social network, it’s an easy one-stop-shop for collecting all of your data.
If you do any activist work – whether fighting injustice, exposing wrongdoing, or supporting freedom of speech – you can bet that at some point in your career, you will have a file, and possibly some digital surveillance to go along with it. This isn’t tin-foil hattery; governments regularly investigate anything they view as a threat, and people trying to change the unjust status quo are threats. The more fractured, fragmented, incomplete, and scattered your personal data is, the harder it will be for you to be persecuted for one of your three daily felonies.
Deleting your search history is a small start, it’s easy, and doesn’t hurt. You might also consider getting your email out of google’s hands too – if it’s older than 6 months, it is considered “abandoned”, and can be read without a warrant. You might also consider setting up multiple google accounts and using them for different purposes (docs, mailing lists, etc).
TL;DR: Don’t delete your data for the corporations: delete it for the government.