How to craft it
Work BenchSet bonus
The bonus applies while the helmet, chestpiece and leggings are all worn together.
wood armor with a jungle tax
Three of the wood sets protect you by exactly the same amount, and this is the one that asks you to walk the farthest for it. Rich Mahogany comes off jungle trees, so getting a full outfit means hornets and man eaters between you and the workbench, and neither of those cares about the thin bit of protection you get at the end.
Chop the logs while you are already down there for a bee hive or a shrine. A dedicated logging run this early costs more health than the finished armor will ever give back, and Boreal Wood or Palm Wood will do the identical job from a much safer biome.
when to take it off
Treat it as day one padding. The first ore set you can smelt beats it outright, and it should already be gone by the time you are cracking shadow orbs or crimson hearts.
What outlasts the stats is the color. Dark red boards sit well against stone and gray brick builds, so it is common to keep the pieces in the social slots long after the defense stopped counting for anything.