Grishka, Are you a mandolin player, or have you played in a group with a mandolin player? I can't imagine playing my solo and then standing and waiting till it's my turn again. The chop chord of the mandolin is an important part of much bluegrass and old time music. I'm sure that David Grisman, one of the world's most respected mandolin players, was not simply strumming the strings to give a good visual effect.
Playing jug band or blues mandolin I will sometimes play a tremolo counter melody or hit double stops, but even in this genre I will often strum chords.