Why is triangle recommended?

I am assuming because it makes the creation on the channel swaps, the rebalancing and the general coordination simpler & faster. 

Also because from my understanding, larger geometries (square, pentagone) don't offer significant benefits over the triangle. Perhaps in the larger geometries your node will be a little better connected but the payments you will be forwarding will have a longer path to follow and require more fees.

Triangles provide 90% of the benefit and is the fastest and least risky to build, because there are less participants. The only time when larger geometries are beneficial are if you're trying to connect a group of friends for example, and you want to minimize the channel opens and maximize connectivity. Also, when you are opening large channels and you want to be connected to other nodes with similarly large channels with a single channel open. In every other case triangles work better.

Thank you for answers!

Very informative!