Libag nga yun. Better to remove it. It does not damage the fret board but it does the strings. If you want your string to last a bit longer, remove them. Also, clean your strings, fret board and guitar after each use. The libag is a result of the guitar (the strings and fret board especially) of not being cleaned after playing. That way the strings last longer, your guitar will appreciate in value. There is nothing better than a clean well kept guitar. Basahan lang ang kailangan.
FWIW