PPRuNe Forums - Mode S and the 1000 code at LHR

Guys,
In the LHR aerodrome booklet, under the Mode S bit, it says that pilots should select code 1000 on the transponder -before- switching the transponder off, whereas our company's SOP say to switch it off and then enter 1000.

Just wondering whether it makes any difference to you from an ATC systems point of view? LHR is the only place I've seen the note, so I'm guessing it's to do with some system you guys use.

(I was under the impression that it was necessary to select 1000 to log the callsign out of your system or something but stand to be corrected....)

Any ideas?
FF