As a rule I write in ink. It sharpens one's concentration. Erasure gives you the illusion you're going to make a more meaningful solution. If Beethoven wrote in ink he would have had an easier time of it.
(Give my Regards to Eighth Street, 207)
I work with a pen and that's a very interesting phenomenon because when I work with a pen everything is crossed out. Some pages there is nothing crossed out and it's usually those pages when there is something of a continuity.
I have always found it more beneficial to experiment with fountain pens than with musical ideas.