A live room has a great deal of reflectivity, and hence a long Rt-60. A dead room has little reflectivity and a short Rt-60. Rt-60 measurements are most useful in determining the acoustic properties of larger spaces such as churches, auditoria, etc. In smaller environs the Rt-60 measurements become so short as to be useless. In these confined spaces, individual reflections from nearby surfaces dominate the sonic picture and are the primary focus for the audiophile.
Reflections can be both desirable and detrimental.
This depends on their frequency, level and the amount of time it takes the reflections to reach our ears following the direct sounds produced by the speakers. Our brain blends together all of the sounds reaching our ears within 5-30 ms of the original. Reflections arriving approximately 30-50 ms or more after the original will be perceived as separate sounds. It is these initial reflections that are most important to the brain in determining the apparent size of the listening room. By manipulating the ratio of direct vs. reflected sound, we can fool the brain into thinking we are listening in a larger room than actually exists.