Advantages of an endoskeleton include strong weight-bearing properties and even growth, while disadvantages include less protection and leverage for muscles. Endoskeletons are generally found in larger animals due to better weight support, as exoskeletons can limit growth due to weight.
An endoskeleton refers to an internal skeleton, as opposed to an exoskeleton which refers to an external skeleton. Being internal, an endoskeleton can support greater weight without becoming too heavy for the organism. An exoskeleton will eventually become impractically heavy for an organism, thus putting limits on size. Also, the endoskeleton can grow with the organism, unlike an exoskeleton which requires regular molting as it is rigid and does not grow.
Being internal and covered by muscles and tissues, an endoskeleton offers little protection to the organism. There are also less rigid areas for muscles to pull against, resulting in less leverage.