In compact view, you’re able to see more spaces at a glance when you’ve joined lots of areas.

The space icons will be smaller after switching, and the team name will appear next to the space name for any team spaces. When hovering over a long name or space, you will see the full name.
Windows
Select the Appearance > Compact View option from the menu by clicking the button This can also be changed in the Settings menu by selecting the appropriate option. You can do this by clicking the profile picture in the app header, then going to Settings > Messaging in the app. Check the box Show compact view on the Space list and make sure that it is checked.
Mac
In the Appearance menu, click Show compact view, then click. The Preferences menu can also be used to change this setting. Once you click on your profile picture in the app header, you will be able to access Preferences > Messaging in the menu that appears. The compact view can be accessed by checking the Show compact view box in the Space list.
Web
Select Settings from the drop-down menu next to your profile picture. Make sure Compact view is selected under Space List in Messaging.