I usually give Philip Schaff a hard time, but let’s be honest – the ANF and NPNF series of translations (the former edited by Alexander Roberts and James Donaldson, the latter by Philip Schaff, and later with Henry Wace) – were amazing feats of translation and publishing for their times. They were, for the English speaking world, the Migne of their age, and animated with a little bit of the spirit of Migne, I would say. Let me quote from Schaff’s preface to the NPNF series 1:
My purpose is to furnish ministers and intelligent laymen who have no access to the original texts, or are not sufficiently familiar with ecclesiastical Greek and Latin, with a complete apparatus for the study of ancient Christianity. Whatever may be the estimate we put upon the opinions of the Fathers, their historical value is beyond all dispute. They are to this day and will continue to be the chief authorities for the doctrines and usages of the Greek and Roman Churches, and the sources for the knowledge of ancient Christianity down to the age of Charlemagne. But very few can afford to buy, or are able to use such collections as Migne’s Greek Patrology, which embraces 167 quarto volumes, and Migne’s Latin Patrology which embraces 222 volumes.
The ANF/NPNF series, dating from the end of the 19th century, has now passed out of copyright, and been promptly digitised and made available in a number of places. It is also readily available in print volumes in libraries. And so it is now the most readily accessible translation of patristic texts available to most English-language readers.
Which is both its blessing and its curse. Because, just as with Migne’s PG and PL, and as similarly with, say, the Battles’ edition of Calvin, time is not its friend. There are better, more recent trnslations that deserve to be read, but they generally won’t be by most, because they cost money, and they are not digitised. I know that, even for myself, the quickest way to look up a patristic text covered in the NPNF series, is to use NPNF rather than anything else.
I’m not sure there is any easy solution to this, beyond the ongoing, vast, complex challenges fcing the ‘publishing industry’ in an increasingly post-print age. It is, perhaps, increasingly possible that we could make public domain or at least Open Access translations available free, online, for widespread use. Indeed, that is exactly what the texts that Roger Pearce’s tertullian.org site holds. And yet, of course, translation takes time, it takes developed skill, and in this case it requires the translator to forego both the financial gain of selling a translation, and the academic-prestige ‘profit’ of producing a translation for an academic market (e.g. monograph/series/journals/etc..).
Hence the Schaff paradox – we will all keep using Schaff et al. because it’s free, it’s accessible, even though it’s not best. Because free and easy will win almost every time.
 Philip Schaff, ed., “Preface,” in The Confessions and Letters of St. Augustin with a Sketch of His Life and Work, vol. 1, A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, First Series (Buffalo, NY: Christian Literature Company, 1886), v.