Most audible errors are introduced because a given disc cannot be read. So, in this case, the drive has to apply error correction, or slow down, or reread. Maybe it does all 3.
It is when the drive tries to correct an error that problems may arise. In bad situations, the drive has to guess what data was there, and it may not make the same guess every time. (This is what SeÃ¡n mentioned). This affects accuracy, but hopefully does not make anything sound bad for casual listening straight from the disc.
A different cause for an inaccurate rip is if the drive returns extra silence at the beginning/end of a song, OR if it cuts a tiny part of the song off. That should not be a big problem for casual listening straight from the disc, though some music players introduce a pause between tracks.
Generally, none of this affects how you hear it while it is playing back. If you hear a pop or a click, you would probably hear the same pop or click when playing it back on a standalone CD player. That is when you try to rip the CD, in the hopes that you can get a perfect copy that will work better. And THAT is where the "accuracy" matters more.