Is there a problem with caching large number of files.?

I have a pretty big site (Coded around wordpress) with more than 500,000 pages. I’m planning to use super-cache for my whole site, WILL THERE BE A PROBLEM if I cache all the pages and store them in a folder /cache/ ? Will there be a delay in serving pages if cache folder is bigger, though all the pages are static ?

On wp-Supre-Cache options page they have said: “Checking for and deleting expired files is expensive, but it’s expensive leaving them there too“. What does “leaving the files there is expensive” mean?

I have an unlimited disk space in my account? Could you please explain how leaving the files on hard disk could affect?