Google's new Data Saver extension for Chrome helps you reduce data usage by compressing the pages you visit. It could come in handy if you sometimes go online from your laptop via a mobile hotspot or your smartphone.
Once you install the extension, it starts working immediately. I found little noticeable difference in the quality of images after installing Data Saver (one of the trade-offs with using compression), but it looks like the extension can reduce as much as 45% of your data usage.
Data Saver is currently in beta and doesn't support secure (HTTPS) pages or incognito pages. It's available already on Chrome for Android and iOS.