Apart from the technical exercises of his that I've studied, I don't know whole lot about Carl Czerny. I know that he never went on tour, that he lived alone with his cats, that we was the student of Beethoven and teacher of Liszt. I also figure that, as one pianist pointed out, the volumes of dry piano exercises he composed can only be explained by a hatred of children.
Speaking of Czerny's compositions, I read once that he worked so quickly that he would compose several pieces at once, so as to work on one while the ink on the others would dry. I sometimes think about this story when students come to me after a week with only a few measures of a piece learned. I wish they would "let the ink dry" in their practice sessions, just like Czerny did with his composing.
Often a student will become so determined to perfect a certain line of music that he will spend hours and hours repeating it, to the exclusion of the rest of the piece. Now, I'm completely in favor of focused repetition, but past a certain point it becomes inefficient; your memory isn't identical to a computer in the sense that you can simply program something in and the job is done. By some mechanism or other, your subconscious needs time to "digest" all the data you feed it. (Of course, if your work is systematic and focused, there's no doubt that this digestion won't take as long.)
Part of good practicing is developing a sense of when you need to move onto a different section and let things simmer. At the same time, moving between sections means you'll be more tempted to slop through large parts of the piece. So, a lot of discipline is necessary when shuttling back and forth like this. One method I find helpful is to make a note of what I've practiced and how. Then I can let this section sit overnight and pick up where I left off a day or two later. Meanwhile I can focus on a different part of the piece and let things settle in.
If you want to try this, be sure to plan your practice sessions ahead of time so that you aren't trying to plan what to practice while you are actually practicing it. Then as you move around, don't go so fast that nothing at all sinks in, but get a feel for when you've reached a point of diminishing returns for a certain section. Take some notes on what you worked on and move to the next section. I think you'll find this style of practicing to be far more productive over the course of several days.