Mulching creates a dense mat that harbours mold, disease and varmints. I do re mow most of my clippings as they are discharged onto unmown areas. When finished, a few passes with the sweeper and Done. I haul mine to the forest nearby.
The two statements in quotes in my post were originally made by churchill in his post #24. I was agreeing with what I quoted.
I think your comment is not universally true and would indicate some combination of the mulching being very course (perhaps due to tall or dense grass, mower travel speed being too high compared to blade speed, or incorrect blade being used, or something else in the design or condition of the mower being marginal), uneven spreading of the clippings (some areas of heavy deposit of clippings covering and overwhelming the blades of grass it lands on), and/or the rate of decomposition of the clippings (determined by such things as unmulched quantity and particle length, pH, nitrogen content, and perhaps other factors that I'm not aware of).
As I mentioned earlier, I highly favor the dual blades per spindle (crosscut) setups and higher blade speed setting on my mower because that gives a finer degree (smaller particle size) of mulching, favoring decomposition at a higher rate. That lessens the likelihood of thatch buildup that you describe.
FWIW, I have read that fescues are generally less prone to thatch buildup than other grasses (some "experts" say that fescues usually do not need dethatching), which means that they are less prone to some of the matting and disease problems you described.
I have had mowers in the past that did not mulch well, and experienced some of the problems you described - had to go back over some areas a second time - not to cut the grass again, but to redistribute the clippings that were previously dropped in clumps in small areas (often happened when the grass was seasonally growing thicker due to cooler weather, more rain, etc., or I had allowed the grass to get a little too tall before mowing, which overwhelmed the deck in trying to keep up with how fast it was pulling in more volume to be chopped up). I never have the problem anymore with the mower I now have - again, because it does a much better job of mulching even if thick or tall. I generally can't even find the clippings after mowing. Before, I didn't have to look for them - they were staring me in the face in little piles.
EDIT:
I know I'm being long-winded already, but here's something else to consider:
I could be wrong, but I get the impression that you are using side discharge.
When I got my current lawnmower (2 years ago), I had the option of installing the side discharge chute or letting the spring-loaded block-off piece swing down over the side discharge opening.
With side discharge, a lot of unchopped or incompletely chopped clippings get blown out over the yard -and that's exactly what I experienced before, especially in an overload (high volume of grass - thick and/or tall) situation.
With the side discharge blocked off as designed for complete mulching, the clippings are trapped floating between the blade plane and deck ceiling (rather than being able to escape unchopped out the side chute) and they get chopped up pretty fine before they drop below the blades onto the newly cut grass. The mower has the power snd the blade speed to handle the higher throughput fully mulched.
