The latest Spotify Desktop update has changed the UI substantially. One of the main downsides is that it is far less responsive than the "classic" UI when scrolling through large playlists.
In the "classic" UI, displaying the track data (title, artist, ...) was almost instantaneous, even on list of more than a thousand tracks. Now, there can be a few seconds of lag to have the data rendered, which makes it more difficult to scroll (even on a decent machine).
I suspect some of this is due to the artwork which is now always displayed for each row within the playlist. Some people may find this useful, but I'd rather not have it if it degrades the performance. If we could have the option to hide it, that would be an improvement.