That, but also the simple deferred calculation approach is orders of magnitude simpler. It is something we could have in the short run: dusting off IrrationalExpressions.jl or creating something similar is a relatively simple undertaking, but an RRA approach would take much longer I guess. (But if anyone wants to do it, that is great too).
It seems to be more CAS-like, and in the type domain, with all the related advantages and disadvantages. My understanding is that the motivation is different, but I have not read the whole source thoroughly.