Purpose
Cool down a build plate quicker than in the 3d printer
If you are less patient and want to remove your fresh printed parts as soon as possible, you might need a cooling stand like this one - perhaps with an additional fan to be placed under the plate.
This might not be a good idea for prints with filaments that are notorious for warping, but for PLA this seems to be fine.
Print
You'll need support for one of the parts, but the removal should be quite simple - at least with tree support. I used cubic infill and - just for fun - Hilbert curve for the top layers.
Assembly
Straight forward. Just put both parts together (not much ways to do it wrongly) when you need them. When not needed, they can be stored in a space of 14 x 8 x 3 cm³.