Well, yeah, there's spam detection and similar features that are enabled by not having client-side encryption. If all of the features that are enabled by cloud-based email aren't worth it to you, fine, but most people like them and you have other options.

The “you have other options” closing is unproductive, but I concur that there are plenty of valid (useful) reasons to analyze customer data. Additional features: phishing and virus detection, suspicious account activity, building private search indexes, cataloging photos by vision results, and using user feedback to correct models.