It's a feature to be able to run more realistically or declutter a yard or complex interlocking. I was going to say the same things as oldman777 and pware, but they were faster on the keyboard. It is great to hide the arrows for things like screenshots and immersive operations, but if you are just messing around, testing, doing switching problems, or trying to troubleshoot stuff I find it's great to have the arrows on. Don't be afraid to muck about in the menus (just KISS and know where to revert to/document where you start from).