I have a mulching mower that does a good job of converting the clippings into tiny pieces, but it still leaves some clippings behind. I usually leave them and let nature's cycle of decomposition take over.
The one downside I can think of is that if the grass was too high and there are too many clippings in one area, it seems to smother the rest of the grass if you leave the clippings. In that case, you may want to spread out the clippings over a larger area.
If it looks like I have nothing but piles of clippings scattered in random spots across the lawn, I do rake them. That is usually if I let it get too high before I mow.