It's not often that we'd do this (and I'm not the person directly involved in adjusting the scale there), but I can tell you why we'd do it.
It's important to say that new communities should be mostly self-moderating from the start - this is a corner stone in our philosophy of how community-driven sites should work. We lower the privilege bar quite a bit during the private beta phase, and then raise it somewhat considerably when a site goes to public beta.
Once in a great while, voting doesn't catch up with the sliding privilege scale, and we're left with a bunch of engaged users that would edit and cast close votes but can't because the voting / view velocity on their posts just isn't sufficient for them to gain more privileges in a timely manner. Hence, lowering the bar a bit as a band-aid for a short amount of time while folks gain enough rep to be effective on the standard privilege scale is a handy way of addressing this. It's not meant to be a long-term solution, just a quick fix for a (few) months until a solid group of folks climb up in the 1k - 3k rep brackets.
Current examples of where we'd do this are exceedingly rare, there aren't any more SE 1.0 sites that need to join the network, and new betas as of late haven't seen problems caused by a lack of voting, but that's where we'd theoretically do this. Edge cases and very niche topics sometimes need a little extra help.
The community critter in charge of watching over Quant SE is taking a look now to see where things stand, and if they're ready to return to a standard privilege scale.