Things to consider before registering as an RYT
On your own ~ and for the vast majority of places holding yoga classes ~ you do not need to be registered with Yoga Alliance to teach yoga; nor is there any kind of license needed to teach yoga. In fact, you can teach yoga without even having a certificate; but it is for this reason that Yoga Alliance came into being; which was probably a good idea at first -so that people without any training are not out there hurting unsuspecting students. But, unfortunately, YA hasn't really curbed that possibility much at all. Most of their work really just seems to be around collecting dues; and fishing for copies of certificates from new yoga training graduates. With this copy they confirm to potential employers that you have a certificate and are a yogi in good standing; but being in "good standing" really just means that you have paid your membership dues. Yes, trainings have to register with them and pay their dues as well. But YA does nothing to see if all the places registered with them are actually meeting their criteria; and the criteria they have is as widely disputed as the world's religions. And, yes, presenting your certificate to an employer is something you could do yourself. But YA wants you to believe that they should do that for you, and that you should pay them about $115 to set that up; and then about $65 a year thereafter. Nevertheless, there are a few employers (or so I have heard) that do require you to be with registered Yoga Alliance, but that vast majority do not. However, if you do have your eye on a very particular studio that you would like to teach at, then all you need to do is ask them if they require you to be registered with YA. Most likely they will not, but the question will be settled quickly in this case either way.
Having said this, probably half of new training graduates do register with YA, but this is mainly because they think they are "supposed to," but after a about a year or two of paying their dues to them they realize that they can just show any potential yoga studio employer their yoga training certificate themselves.; and thus stop paying those useless annual fees.
My estimate is that probably more than 70% of the places that hire yoga teachers do not care if you have registered a certificate with Yoga Alliance. But honestly, at present I cannot think of any place where yoga is taught that actually requires it; not even the YMCA or the Integrative Medicine wing at Bethesda Hospital where I both taught regular classes and directed a yoga teaching training. Nevertheless, I assume there must be some health club employers out there somewhere (and maybe even some yoga studios) that actually do require you to be registered with YA. But usually such places do not specialize in yoga and have no way of assessing if a yoga teacher has any skill. Therefore they might want to see if you are a card carrying Yoga Alliance member. Nevertheless, this still doesn't actually prove a teacher has any actual skill. Thus, most reputable places that hold yoga classes (including the YMCA) require a teaching audition; wherein you are asked to teach a class while being observed by another yoga teacher, or fitness instructor, with a trained eye. They do this because they know this is the only way to tell if a teacher truly has any actual skill.
On the other hand, i have seen many teachers who are registered/approved with Yoga Alliance and yet seem to have no real grasp of the practice or teachings at all. Nevertheless, they remain as approved RYT's (Registered Yoga Teachers) for as long as they keep paying their annual fees. Thus, with Yoga Alliance money is the determining factor as to whether someone qualifies as a yoga teacher, not any actual skills.