Point of an IFC?

[DeAngelo]

So my custom story is slowly but surely nearing completion (it's pretty much done as far as being able to click new game and make it to the credits, now I just have to make it purty) and I find myself wondering about Isolated Full Conversions. I have some questions:

1: Is it too late to make mine into one? Or is that something you gotta kinda do from the get-go?

2: What are all the benefits of making one? The reason I never bothered is because from what I gather the benefits are as follows:
*Ability to change default movement speeds (which I don't see the point of unless you're making a goofy sanic gotta go fast level, and besides can't that stuff be changed via scripts that run on map start?)
*Ability to change the lantern, which is neat but not really necessary.
*Ability to change the menu background and inventory, again cool but not that big of a deal.
*Ability to modify things like sanity damage from looking at goobers or being in the dark. This one I can see being helpful, but I never needed it.

So are there any other cool things an IFC can do that I don't know of? They seem like more trouble than they're worth to me, as I've played over 40 custom stories which all worked fine but had 3 seperate IFCs not work for me despite trying everything people suggested.

Also, sorry for being annoying. I'm a curious man by nature and I tend to just ask whatever pops into my skull.