What does this fuse do.

[Bobgriff]

Under the car today whilst it's off the road and on axle stands just checking out the chassis for rust and rectifying as I go when I noticed for the first time a blade fuse just above the main 100A fuse. It's a 25A fuse and I have no idea what it does? Also looks pretty open to the elements.

So, any ideas what it does and should it be better protected from the elements?

Thanks in advance