Announcements are an incredible way to let your entire clientele (or a certain group of clients) know something all at once.
A few examples would be:
Your gym being closed on short notice
Your sick and all workout programming will be late
You have a vacation coming up and won't be reachable for a few days
They are easy to set up as well. From the top dropdown, you can select Add Announcement and then choose a duration, client type, and even a video link to go along with it.
Once the announcement has been assigned, your clients are able to see the message right at the top of their home page. It will be pinned there until the announcement expires.