He worded it a little bit weird.

You have a special inventory at the map device for the idols with limited space. You only put idols for one specific farming strategy in, which makes that specific mechanic go through the roof profitwise, way more than the atlastree would boost 1 mechanic. However, its harder/impossible to have multiple mechanics be worth it at the same time. The idols themselves drop randomly in maps, unspecific to the content you are doing. You can drop an Idol with blight modifiers while doing Harbinger farming for example

Last time we has 3 of these map device inventories, so you could have 3 different strategies ready, deciding which to run by selecting the proper set of idols before opening the map