The downside, sometimes, is that you forget why you put stuff in.
True, if something on the revision pass looks incongruous, it's probably a problem. It does not, however, mean that it can be excised and thrown away. It may need to be reworked. Or relocated. Or replaced with something else only resembling it in structural function -- to contrast with something else, to motivate, to explain a needed detail.
The thing is, it can be really hard to notice that when you forgot what happened next. If it's to set up the next line of dialog, excising it can be fixed quickly. If it's a scene or two -- or three or four -- later, it can be harder. Especially when considering whether a whole scene ought to go, being unnecessary, or at least not pulling its own weight for its length.
Most of the time I have enough of the plot in memory that I can remember. To be sure that means the old has a magnetic attraction to it because I know what to expect. . . .
The delights of a writer's life.