What will happen if the reverberation time in a big hall is too long? How can we reduce it?

Reverberation is the persistence of sound due to repeated reflection, where an echo may be heard. We can reduce the reverberation by covering the roof and the wall of the hall with sound absorbing materials like Acoustical panels, Noise and sound isolation foams, MLV (Mass Loaded Vinyl) Soundproofing foam, etc.