YouTube announced YouTube Go back in 2017, when it was released to India and Indonesia as a light weight version of the main desktop and mobile app versions. It was designed to run better on devices with less processing power, such as entry level laptops and smartphones. It also had an easy way to control how much data would be used, useful for expensive plans or slow carrier networks.
In 2018, YouTube rolled out the app to 130 countries, and was only 10MB in size. However, in a few months YouTube will be discontinuing the app, instead advising users to download the main YouTube app, such supports more features. YouTube explains that since the Go app was launched, there are a number of performance improvements been made to the main app.
For those users where it is critical to control how much data YouTube uses, the company has said that soon there will be new controls added to manage this.