The idea is to use that information to "build a more tailored experience," the San Francisco company says. That figures into determining which targeted ads and other promoted content to show to each user. Other uses include suggesting accounts for the user to follow based on shared interests, Twitter says.
Twitter says it is collecting only a list of the apps installed on the user's Android or iOS device, not data from inside the apps. That means the company would know you have, say, ride-sharing app Lyft, but it wouldn't know where you're being driven, how you pay for the rides or whether you're using Lyft at all.
A prompt will notify each user before the data collection begins, Twitter says.
To opt out, turn off the "Tailor Twitter based on my apps" feature by following the directions posted at https://support.twitter.com/articles/20172069.
The feature has not yet been rolled out to all users.