Consider the situation where a Note On event is triggered while the note is actually playing.
Now you will have two Note On events followed by two Note Off events, which might give unpredicted results.
There are several solutions to this problem. These are graphically shown below.
Below:
x = Note On
o = Note Off
Original
x----------------x----------o----------o
Solutions in MIDI Note Event Cleaner:
Break First Note On AND Use First Note Off
x---------------ox----------o
Break First Note On AND Use Second Note Off
x---------------ox---------------------o
Discard Second Note On AND Use First Note Off
x---------------------------o
Discard Second Note On AND Use Second Note Off
x--------------------------------------o
Move second Note On to right after first Note Off
x---------------------------ox---------o