Yes that is part of it. I stole this image from
@Benuser. Sharpening without thinning will lead to a progressively thicker knife over time. This change in blade geometry can affect performance. This can take a dozen sharpening sessions to notice and then once it happens it's a pain to fix.
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But the other more immediate concern with touchups is that a fine stone does not cut fast enough to keep up with accumulated damage at the micro bevel level. So when you stop getting the same pick me up from your fine stone you drop down to a coarser stone to reset the cutting bevel with fresh steel.