It's quite tricky to record an instrumental synth line first 'pop' - you might hit a bung note, not get it rhythmically perfect, or you might start in the wrong spot - e.g start at beat 3 thinking it is beat one.
It's then a bit tricky to just delete what you just did and do a new take - especially if you're in keyboard mode and say, 64th note zoom quantize mode. In that case you've got to switch back to track mode, switch the zoom to a smaller zoom level, scroll up and down to find all the notes you hit to delete them, then return the zoom to your desired setting and finally re-enter keyboard mode. If you get the take wrong twice in a row this gets a bit frustrating.
If there was an instant 'undo' command that worked like Ctrl Z on a computer - it would make recording takes a bit more fluid.