If you know every name and syntax of every command off by heart then you might not have a use for it, but for beginner to intermediate scripters they can be very useful features.
For example, a newbie might think that sockets have to be "ended" or "exited" rather than "closed", thus using /sockend or /sockexit rather than /sockclose
That's just one example, there's plenty more though..
/hadd -> /happend
/hfree -> /hdelete|/hdestroy
Most "intelligent" code completers will also tell you what parameters go with the command/identifier too, thus making it much easier to know exactly how to use the command and save you having to open the help file to check.