m0n0wall is a firewall, and the purpose of a firewall is to provide security. The more functionality is added, the greater the chance that a vulnerability in that additional functionality will compromise the security of the firewall. It is the opinion of the m0n0wall founder and core contributors that anything outside the base services of a layer 3 and 4 firewall do not belong in m0n0wall. Some services that may be appropriate are very CPU-intensive and memory hungry, and m0n0wall is focused towards embedded devices with limited CPU and memory resources. The non-persistant filesystem due to our focus on Compact Flash installations is another limiting factor. Lastly, image size constraints eliminate other possibilities.
We feel these services should be run on another server, and are intentionally not part of m0n0wall:
Intrusion Detection/Prevention System
Packet inspection at any layers other than 3 and 4
A general purpose web server
An FTP server
A network time server
A log file analyzer
For the same reason, m0n0wall does not allow logins: there is no login prompt at the console (it displays a menu instead), and no telnet or ssh daemon.