Its sole claim to fame is that it was one of the few manuscripts used by Erasmus in constructing his Greek NT (1516), and that it contains a clumsy scribal gloss, (which in turn sparked Erasmus' famous annoyed and skeptical remark about Greek manuscripts). John Marsh describes the gloss:
"The common text at 2 Cor. 8:4-5. is ...δεξασθαι ημας (v5) και ου καθως ηλπισαμεν... but the best, and most numerous authorities reject δεξασθαι ημας , which is probably an interpolation. The proprietor of an ancient MS. from which Corserdoncensis was copied, knowing that δεξασθαι ημας was contained in some MSS. but rejected by others, and wishing perhaps to rescue these words from the charge of spuriousness, wrote, with a reference to δεξασθαι ημας the following note in the margin : εν πολλοις των αντιγραφων ουτως ευρηται. The industrious scribe, who wrote Corsendoncensis, taking these words for a part of Holy Writ, which had been omitted in the text and supplied in the margin, transferred them into the body of his own work, and wrote as follows; ...δεξασθαι ημας (v5) εν πολλοις των αντιγραφων ουτως ευρηται και ου καθως ηλπισαμεν..." ( Marsh's Letters to Archdeacon Travis, P. 176 noted in The Critical review, or, Annals of literature, Volume 16 [Feb. 1796] edit. T.G. Smollett, p. 450)
Jan Krans tells us:
"The reception history of the scribal blunder itself is interesting as well. It was mentioned for the first time by none other than Erasmus. In his 1519 edition, he added a long note to his annotation on these verses. The example must have been very welcome to him, for it is clear proof that even the sacred texts are not free from ridiculous scribal errors and that textual criticism is necessary, whatever theologians may say. He concluded the note by saying that 'we found innumerable places corrupted for this same cause'. Even before the 1519 edition, he had already mentioned the case in his apology against Faber Stapulensis. There, the point made was somewhat more specific. He warned his colleague to 'not naively trust (Greek) manuscripts. Keep thinking critically'. "
This remarkable statement by Erasmus is important, because he never produced any further examples from the "innumerable" instances he claimed to have found. There plainly aren't that many in the few manuscripts he himself collated (certainly none like the blunder in GA-3).
From this seed of Erasmus, the rumour-weed about scribal glosses begins to grow:
"In subsequent centuries, the blunder was frequently mentioned in text-critical books. Bengel, in his 1734 Greek New Testament, refers to Erasmus. Metzger also mentions the case in his Text of the New Testament (3-1992, p. 194; see also Metzger/Ehrman 4-2005, pp. 258-259), referring to Bengel." (- Jan Krans, Weblog 2010)
Yet the fragility and weakness of this claim is apparent, even to Jan Krans:
It is ironic that Erasmus, often hailed as the 'father' of the Textus Receptus turns out to be the ultimate source of the dubious generalization that "scribes frequently tended to mistakenly turn marginal notes into text", and that this maxim is actually based on a single late 12th century miniscule.
"The example ... shows that marginal annotations which were mistakenly adopted into the text did occur. The question remains, however, how widespread the phenomenon actually is, and how it can be demonstrated in cases that are less clear than the one in miniscule GA-3." (- Jan Krans, ibid.)
For Jan Krans' article, see here:
Jan Krans on GA-3