Just an example to hide JOIN PART and MODE's for channels with atleast 100 users. Am sure you could look in the helpfile for more info
Code:
alias largechannel return 100
on ^*:JOIN:#:{ if ($Nick($chan,0) >= $largechannel) { halt } }
on ^*:PART:#:{ if ($nick($chan,0) >= $largechannel) { halt } }
on ^*:RAWMODE:#:{ if ($nick($chan,0) >= $largechannel) { halt } }