There is a pretty good consensus that the benefits from only using a primary outweigh any benefits from moving to secondary/ Of which there are none. Your beer will clear up just fine. As an example, the brown ale I won 2nd place with was noted in the judging sheet as being clear. I have never used a secondary other than when I added fruit. As far as why not use the extra carboy you have, although probably minimal, just using it because it is available is a mistake because anytime you move your beer to another vessel you risk adding oxygen and/or possibly contaminating it. I would leave it in the primary until ready to keg. Make sure you cut an inch or so off the dip tube. After a few pulls it will clear up and within 2 weeks it will be very clear. But to answer your question, you can rack now if the yeast is done fermenting.
Of which there are none? I think that is about as good as saying you shouldn't keep just in primary. I've done some full in primary too and I loved them, but I still use secondary from time to time and have noticed differences in two brews that were identical in all but racking to secondary. Of course I find them especially helpful with adding late adjuncts. Nothing detrimental, but differences sure. Contamination is more possible sure, but highly unlikely, with just a little bit of paying attention. The fears espoused in this forum would have done well with the past few hundred years of beer making. All those guys and monks, at least finally they would learn how to make good beer.
Heck fermenting openly you can make great beer.
The things I have noticed personally in my experiences is that keeping in primary longer tends to help with clearing more than secondary (IME).
The beers that I have kept in primary for longer times then moved to secondary have been clearer than using primary alone. (the beers moved quickly to secondary have been less clear)
Many experienced brewers who decry secondaries are many times keggers who do a cold conditioning step that is like unto it.
Either way produces a great beer, and both ways produce a slightly different beer. I noticed this the most last time I brewed a trippel. I did a 10 gal batch. One I kept only in primary, the other transferred. Same batch, slight differences. The one that I left in primary for a good while then transferred ended up with more clarity, than the one fully in primary. The one fully in primary had great clarity as well though.
Moving to Secondary vessels frees up my primary vessels
I have NEVER had a single issue with infection or oxygenation while moving to secondary, you could, but you could have issues with hundreds of other things too.
I can harvest my yeast quicker since I don't have conicals if I move to secondary.
I understand that people with a lot more experience than me keep saying don't use them, don't use them...but why there is no difference, or no positives? There are, obviously, some of them may just be preference. I am not even saying to use them, and I haven't on all lately, but I feel like it is a pendulum swing in here, of people figuring out autolysis isn't an issue, and then running to the other side saying Don't do it, don't do it. It does you no good, your dumb if you do it. The poster above took no bad tone like that, so don't take offense...I'm just sayin.