What is the significance of playing in 3rds in music theory and how does it contribute to the overall harmony of a musical piece?

Playing in 3rds in Music Theory is significant because it creates a harmonious sound by combining two notes that are three scale degrees apart. This interval is pleasing to the ear and adds depth and richness to the music. By incorporating 3rds into a musical piece, composers can create a sense of balance and cohesion, enhancing the overall harmony of the composition.