Unlike the teak garden bench and gnome bench, this bench cannot be sat on due to rendering issues.[1] Attempting to do so results in the chatbox stating It looks like you'd get a sore back if you sat on that bench. The marble decorative bench suffers from the same issue.
^"The Construction Expansion". RuneScape News. Jagex. 25 August 2016. Archived from the original. "The teak and "gnome-style" mahogany benches can be used as seating, though regrettably the marble and obsidian models would have horrible render order issues if you merged with them, so they're just for decoration."