Although these one here do it, there's also an equal number of people on here who don't, and don't have a problem with their beers not turning out.
I don't think it's gonna matter either way, because the beer you are racking over is wrapped in a blanket CO2 anyway and is going to purge the O2 up and out of the secondary as you are racking. That's one of the reasons we rack from bottom to top...it pushes the O2 out.
Also the act of racking will get the yeasty beasties going and they will produce some additional CO2 all by themselves...that's why a lot of n00bs panic and post that the airlock in secondary is bubbling.
Having said that if you have the capabilities to do it, then go for it...it won't hurt. It's kinda like sanitization...There's no such thing as too much.
But for any n00bs watching, you DON'T have to go out an buy a can of CO2 in order to rack or to make good beer....You can, but it is a preference, not a mandatory thing.