At LGW, we only provide a marshaller when the stand entry guidance isn't configured for the aircraft type or where FOR THE CONVENIENCE OF THE OPERATOR, the aircraft is required to be positioned nose out. On many stands, positioning has to be within a tolerance of 600-900 millimetres to ensure that the aircraft is safely within the confines of the stand AND that all the services, fuel, electrical ground power, airbridge etc will fit. It's a LOT more than just not hitting the Terminal building!
Positioning an aircraft nose-out, especially when space is at a premium and several a/c of differing sizes need to be parked adjacent to one another (and taking into account minimum safety distances between a/c and order of departure etc etc) requires great skill and an excellent working knowledge of various aircraft dimensions, turning circles etc.
Some pilots just don't seem to get any formal instruction on how to comply with marshalling signals and make a right hash of driving the a/c. Our lads and lasses are very patient and are taught how to cope with these situations, but many years ago we did have one individual (now no longer with us) who ended up throwing his marshalling bats at a particularly dull pilot. Wouldn't happen today!
TheOddOne