OnBeforeConnect

Would execute immediately before connecting to a server, if alias exists.

An example 1: ALIAS ONBEFORECONNECT "exec mysettings.cfg"
An example 2: ALIAS ONBEFORECONNECT "r_wateralpha .4; r_drawviewmodel 1"

Why? There are some servers that send certain aliases and settings to clients and it would be nice to be able to wipe those clean. For instance, some servers force r_wateralpha to 1 for the duration you are playing on them.

Some servers set impulse aliases that are undesireable on other servers. Some versions of Rocket Arena set r_drawviewmodel 0 while you are "on-deck" and then if you connect to another server, it's still 0.

Making it an alias would allow the user flexibility to what it does.

OnIntermission

Would execute OnIntermission alias, if it exists, when intermission hits:

An example 1: ALIAS ONINTERMISSION "screenshot"
An example 2: ALIAS ONINTERMISSION "status"
An example 3: ALIAS ONINTERMISSION "status; ping"
An example 4: ALIAS ONINTERMISSION "say I own all of you!"
An example 5: ALIAS ONINTERMISSION "exec fancy-name-animation.scr"

In a single player game, you could have it automatically take a screenshot when you are done with a map recording kills/secrets/time.

In multiplayer, you might want a screenshot or you might just want STATUS ... which records your scores and those of everyone else in your qconsole.log.

There are other uses, making it an alias makes it flexible.