My area may be an exception, where this statement has been relevant:
Can I ask though. Only last week did a headmaster of a very popular over subscribed school in the South West tell me that I must put his school first if I wanted any chance of getting a place. This is just bull yes?
There are two schools in a catchment area. Historically, one over-subscribed, one under. Selection is by lottery once the SEN/LAC/Sibling bit has done. If you put School A (oversub) first - you may or may not get a place depending on the lottery - you may get School B. If you put School B first, you will get School B, as they can offer places to all who want it.
In this case, the Head of School A would be correct to say that if you want a chance (and it is only a chance in the lottery), to get a place in his school, then you have to put School A down as your first choice.
Having said that, with the pressure on school places, last year both schools were oversubscribed, so for the first time, that advice would no longer be relevant. Some people got offered neither school till they got all cross and the LA forced the schools to take all the extra pupils.