The first 10 levels of the underground are very easy to complete, and every level you get a chest that can contain a 228 weapon or a 268 set piece.

If you have the season pass, It's likely that you have thought about leveling your alts for those free drops. The 10 first chests of the underground are a really good incentive to do it :)
You can level an alt relatively fast doing the pentagon missions, and you can have a 30 alt in about 3 days, easily. Then you only need to swap your equipment to the alt, and in about 6 missions you'll be lvl10.
I didn't thought about this at all, and yesterday I got that set pieces I needed to upper my main a bit :) Easy, and without the need of my crew around!

tl;dr: Every alt = 1 free drop /15d, 10 "easy" chest from underground. A lot of 228/268 items!

(edit) maybe this is to obvious, but I didn't thought about it; and I don't remember seeing it anywhere :)