Occasionally, the rhetorical question is asked of inerrantists: "What's the use of having an inerrant text, if your interpretation of the text is fallible?" Sometimes this question is asked by opponents of inerrance, and sometimes by those who think that those who accept inerrance don't go far enough—they should also accept an infallible exegetical authority. I've done this myself, as an argument for Catholicism.
But the argument implicit in the question is not a good argument without further work. It would be silly to ask: "Why do you care about having a calculator that makes no mistakes, given that you can punch the wrong numbers into it and read the answer off wrongly?" When using a fallible calculator, there are three sources of errors: the calculator, the data input, and the reading of the output. Surely it is a good thing to be able to eliminate one of the three, even if the other two remain.
Furthermore, there is the following advantage to having an inerrant text: progress in interpreting the text is apt to get us closer to the truth of the matter in the subject the text is about. But if the text is wrong on some point, it might be that the better we interpret it, the further from the truth we find ourselves (if we take the text to be authoritative). It is worth having this feature. We might be currently unable to tell what Scripture requires of us in some matter, but it is not unreasonable to devote significant effort into trying to figure it out—because it is likely true.
But let's go back to the rhetorical question and see if we can make it into any argument that can be defended. First of all, it's not clear how "What's the use of p?" even when met with no answer gives us reason to deny p. What's the use of the moon? I don't know, but my not knowing the use for it doesn't seem to significantly affect my confidence that it's there.
However, inerrance isn't like the moon. Inerrance is very unlikely without a miracle. And we might think that God doesn't work miracles except with good reason. So perhaps we could argue that if inerrance is of no use, God wouldn't bother with it. But that's going to be weak. How could we rule out all uses of inerrance? And in fact, surely there are some. The belief that Scripture is inerrant has inspired many people to obey various good commands in Scripture. Moreover, it is better be inspired by a true rather than false belief. So there is surely some use of inerrance. One might worry that the miracle is too great and the benefit disproportionately small. But I don't see why an omnipotent being can't do a great miracle for a small benefit (God helps me find lost objects sometimes—for all I know, he may even be miraculously transporting the lost objects to me, though somehow it seems more likely that he is simply directing my attention to the objects), nor do I see the benefit as small.
Still, there is, I think, some force in the argument of the rhetorical question. There are four sources of errors in information obtained from a text: errors in the original, errors in copying, errors in reading (decoding of words), and errors in interpretation. If it turns out that there are likely so many errors in interpretation that the benefit of lack of errors in the original is quite small, then there is something to be said for asking why God would have ensured a lack of errors in the original without ensuring an infallible method of interpretation. (If a measurement has two sources of error, one of the order of magnitude 0.001 units and the other of the order of magnitude of 0.020 units, a scientist would be unlikely to try to minimize the first error without trying to minimize the second.) But this would require a further argument that fallible interpretation would be quite unreliable—we couldn't just base the argument on the mere fact that interpretation is fallible. Moreover, I think this wouldn't so much an argument against inerrance, as an argument for an infallible method of interpretation (such as a magisterium or tradition or both).
Is it the case that errors in the interpretation of the Bible are so very common that there is something to the argument? I think it might be. Granted, there may be wide exegetical agreement on certain basic points. But if the point of inerrance is simply to preserve agreement on these basic points, we would not need full inerrance, but a more limited doctrine of preserving the truth in the basics (this point was made by one of our grad students in discussion today). So we might still argue: If we think God valued truth in such a way as to give us full inerrance in Scripture, we have good reason to think that he would also have ensured an infallible interpretative method, since that would serve the same value. This is an argumentum ex convenientia, an argument form well loved by medieval theologians.
So, yes, there is something to the argument in the original rhetorical question, but it would take significant effort to defend it carefully. I haven't put in that sort of effort in this post.