Composers can indicate their general intentions regarding damping in the legend of the work.[Inglefeld/Neill 1985]
Always let the strings ring.
Damp whenever possible according to the note values.
"The notation in the whole piece gives attack points in arpeggio sounds. There is no need to damp, or calculate separate durations of notes within a figure, unless written as staccato or damping, as large chords and continuous resonance is wanted. Especially noises, scraped sounds and very deep notes should ring as long as possible. The rhythm gives duration of the scraping or glissando action itself, not the sounding duration."(from the legend of "Pastorale" by Ruben Sverre Gjersten)
A composer's notation can also clearly indicate his/her general intention. Slurs or the letters L.V. ( laissez vibrer/let sound) after a note indicate that the note should be left to sound. Staccato or damping signs indicate what notes to damp.