I hardly ever use these techniques (personal choice) but octaves are especially common with chromatic players playing in various styles (check out Antonio Serrano's flamenco work, or early Toots Thielemans playing jazz). Chords are a bit less common so due to the limited number of available chords in various keys. However, slapping chords used to be very popular, especially among those playing various folk styles in my dad's generation (he would be in in his late eighties now). He learned to play in the army during the second world war and would use chord slapping and octaves exclusively when playing folk, popular, and Yiddish music.
- Slim