Why do you want to have a file that you know you just created? Most of the time when I want that I really want File::Temp. For locking you have other options available, including flock. You can complain that flock often doesn't work well over networked file systems. But sysopen also doesn't work well on those systems.

So yes, there is a task that you can do with sysopen that you can't with open. But I have yet to encounter a situation where I thought that sysopen was the best option.