I rarely transfer to secondary. The only reason I see to transfer a little early, while it is still fermenting like your instructions say, would be so that the continued CO2 production would mix and flush out the air in the headspace. This way, your airlock will trap a nice layer of CO2 in the secondary, which theoretically would help prevent oxidation and infections. I think you would need a lot more air exposure and splashing to cause oxidation. Like the kind you get from needlessly transferring and moving your beer too many times. The simplest thing to do is leave it alone until you're ready to package, unless you have a real reason to transfer it to secondary.