What are the fail2ban limits?

[Linulex]

Even on a server with "only" 175 domains, plesk gives the error:

"Warning: Fail2Ban might not work well if there are many domains and Fail2Ban has to monitor too many log files."

I have asked google but no one seems to know:
what are the limits of fail2ban?
how many is to many?
What will go wrong if the limit is reached? no more banning? wrong ip addresses banned?

regards
Jan