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If you only log in to your Google account at home, and you're the only one who sees your computer monitor, then sure, they're just letting companies target you based on what people statistically like you have bought. For some, that may mean lots of ads for clothes, other lots of ads for adult services.

What if you log in to your Google account at work and at home. Your at-home purchases should not lead to targeted ads at work. Lots of people buy not-safe-for-work items; most wouldn't appreciate related ads being shown at work.

This is only "privacy-safe" if all the computers you use are 100% private, and even then, being lumped together with others based on how you use your computer is still a basic privacy breach. Unfortunately, in this day and age it's not only expected, but accepted.