For years, Chrome for Android has had a Data Saver feature. However, it never worked on secure (HTTPS) pages, so it has become somewhat irrelevant as most sites move away from insecure HTTP connections. Starting with Chrome 73, which is about to start rolling out on Android, Data Saver now supports HTTPS sites.
Google says the new and improved Data Saver "may reduce data use by up to 90% and load pages two times faster." If you still have a good connection, Data Saver will only make minor adjustments to the page. However, if you have an extremely slow data connection (around 2G or slower), and Google estimates the page would take more than 5 seconds to fully load, Chrome will show you a "lite" version instead.
Lite pages are rendered by Google's servers and sent back to you, similar to how Opera Mini works. They might break the site entirely, so Chrome allows users to switch back to the normal version with just a tap. Sites can also opt-out of Lite mode.
The new Data Saver feature is part of Chrome 73, which is already available on desktop and should appear on the Play Store within the next few days.
- Chromium Blog