Sound pressure waves are usually emitted from a source in all directions. In this picture are a few of the paths that these waves could have taken. Sound waves reflect off a surface and produce a resultant wave with less sound energy. This energy loss is due to the material composition of the surface that the sound wave was reflected from. Some energy of the wave is absorbed by the material, some is transmitted through the material while the remaining energy is reflected back into the space it originated from. This results in a decay of sound pressure in the space as the wave is reflected off many surfaces. This decay of sound pressure can become a very important factor in the acoustical quality of a space. If the purpose of a room was intended for speech or communication, a rapid decay of sound pressure would be needed to keep the speech intelligible. Imagine how difficult it would be to understand someone that was giving a speech in a space such as a pool in this figure.
Now, consider a large musical performance hall. In this space, a rapid decay of sound pressure would not be ideal, but rather a slow decay. This creates a very full sound that compliments the music, leaving tones that sound pleasing with the direct sound that the audience is focused on. The presence of reverberant sound gives musicians the ability to create very dynamic performances that are capable of filling the entire music hall and creating a dramatic experience for the audience.