Had a Sim recently where the instructor was adamant about not extending flaps until gear extension was completed. But never got a satisfactory answer as to why.
The answer is in FCOM normal procedures. During approach it says "Flaps 2, when flaps are at 2 gear down". It further says "when gear down Flaps 3". You say Flap2 when the number becomes blue to confirm SFCC has got the order but you lower the gear only when flaps are extended to two. Similarly you announce gear down when you see three reds to confirm LGCIU is lowering it but you only select flap3 when the gear is actually down that's when three green. The instructor was right. Even the Airbus PDP displays the same.