In most cases, rather a pointless function. In 14 years never a help, but sometimes a hinderance. Let's face it, we have flown the aircraft all the way from X (no line to follow), landed, found the stand, and now matey boy/girl is telling us how to follow a nice yellow line (which we can see) the last 30 metres or so. Well, if it wasn't for him/her I'm sure I would have hit the terminal thousands of times (or not). Or maybe marshalling is "Care in the Community", a job creation or a YTS Scheme.