How playlist followers work
A playlist's followers are the people who saved it to their library. Spotify shows the number as saves on the playlist page; it is the same count. It goes up when someone saves the playlist and down when they remove it.
Live, not daily
Play counts move once a day, but followers move during the day. This page asks Spotify again every few minutes while you watch, and the chart under the counter marks every change. Today's and yesterday's change sit next to the count.
The songs on the playlist
Under the counter you see the first 25 songs with their own play counts, so you can tell which songs carry the playlist. Open one in the Spotify stream counter for its daily streams and a live count.
Private playlists and personal mixes
Only public playlists have a follower count. Private playlists, and mixes Spotify makes for each listener (Discover Weekly, the Daily Mixes), have none that anyone else can see.