Those who use Photos on Android should experience faster image backups when they're not connected to WiFi, as the app will automatically save files in a lightweight preview quality first. When a WiFi connection is later detected, Photos will replace these with the full, high-quality versions. The iOS and Android versions of the app will do the same when you're sharing pictures with your friends on low connectivity -- first sending them a lower-resolution image and then pushing the full-quality original over when a stronger signal is detected.
As for the video-calling Duo app, Google is adding a voice-only option so you can talk to your friends without the image stream sucking up all your bandwidth. The company said in a blog post that this feature will "work well on all connection speeds" and rolls out first in Brazil before going live in the rest of the world "in the coming days."
Google's chat app Allo also gets an update to support document-sharing, so those who use the app on Android can send .pdf, .mp3, .apk, .zip and .doc files to each other. This addition isn't related to connection speeds, but it's a handy tool that makes Allo more useful than before. The connectivity-related optimizations for Duo and Photos, on the other hand, are sure to be welcome by those who either have limited data plans or often find themselves in areas with poor coverage.