Too much of anything is bad.
Whenever anything is taken to an extreme, the yin-yang polarity flips and brings its opposite. If you experience a high, like a roller coaster, you will experience a low . . .
Practically, experiencing an excess of amount of pleasure will inevitably make normal living afterward feel extremely depressive and dis-pleasurable by comparison. This can drive destructive pleasure-seeking behaviors, and is the ultimate driver (as one example) of addiction. Addiction ultimately being the loss of free choice as part of a compulsion to avoid experiencing the opposite.
Biologically, you wear down your body through exhaustion of resources in huge dopamine flood of chemicals you send to your brain. This dopamine flood can also desensitize the brain, setting up the addictive cycle.