Timelines can also be removed/hidden in Pro version. Open timeline editor (gear icon on the left side just above timelines), hide Computer usage timeline.

For anyone else who stumbles in here from google, simply trying to reduce the huge height of the timelines: there's a not-at-all evident splitter bar that you can drag up, which, in the Day view, is located right below the hours "ruler". This reduces the height of all timeline bars at once. Beyond that, I agree that it would be useful to be able to shrink some of the bars more. For example "Computer Usage" is pretty much redundant with Applications, so far as I can see.