If you're talking about that bracket on the front weight bracket, my 419 loader has one too. Per the manual, it's called a Latch Plate. I've attached a picture to show you what mine looks like.
My previous tractor, a Deere 670 with a #60 , didn't have this Latch Plate.
Since it's there to hold the front of the loader on, I'd say it's advisable to use it. Never any problems other then occasionally I have trouble pulling the pin when the Latch Plate is in the lowered position (close to the weight bracket).
The #60 loader's masts went into two receptacles and had wedges on both receptacles holding the masts in place. Loosening and tightening these wedges was an extra step in removal and re-installation of the loader. One was supposed to reposition these wedges every so many hours (or daily) to ensure the loader masts stayed in the receptacles.
Never had any problems with mine, but I really don't use my loader that much.
The 419 loader is a bit easier then the #60 was to remove and re-install.
I do look at tractor pictures on the internet (mostly on MachineFinder.com) quite a bit. In fact, I've quite a collection (mostly Deere's with a few others thrown in). Going through those pics to find the one I attached, I did notice some 430 loaders had the Latch Plate and some didn't. I find this curious since all the 4xx series loaders were basically the same design.