This is a minor bug that happens on my laptop which runs a x86_64 Parabola GNU/Linux-libre OS. I have three panels on XFCE screen space, the right most one is a vertical panel with a workspace switcher, a timer (bug concerning), a clock and a calendar.
I use "Deskbar" as Panel Display Mode and the timer plugin is taking up space above and below which is not necessary and expands the panel when there is no point. I think that the user adds expansion separators to expand and thus the plugin should not.

See attached screenshot for an example.