Having an investment portfolio means you are VERY price and feature sensitive, and you have a lot of decision making to do when it comes to renewing/expiring domains. This can be time consuming or just inconvenient timing. Having a cost and feature effective registrar that won't screw you if you dilly-dally a little too long is incredibly important.
One issue I've seen is that certain registrars refuse to give you the auth code once the domain is expired, or they at least make it as difficult as possible. CIRA's form that allows you to request your own auth code is great to get around that - but ONLY if the "lock" feature most registrars have isn't used. If your domain is locked, then having the backdoor to get an auth code doesn't help you, you're still held hostage by the registrar.
This is why as a large portfolio holder it is important to first and foremost, use a registrar that appreciates your business, not one that looks to take advantage of you when the opportunity arises.
This is why I've always been loyal to baremetal, they've never screwed me, in fact quite the opposite, they've looked out for me. If you have a good registrar, all of this other b.s. goes away.