Beta-alanine has been shown several times over to benefit endurance performance and has even been shown to increase repetitions to failure in strength training protocols. However, the literature on beta-alanine having a significant impact on long term gains is inconclusive, but the short term effects make it a worthwhile supplement for bodybuilding training.
Reference: Culbertson, J. Y., Kreider, R. B., Greenwood, M., & Cooke, M. (2010). Effects of beta-alanine on muscle carnosine and exercise performance: a review of the current literature. Nutrients, 2(1), 75-98.