In general all strength is functional to an extent. I will cover why that is not always true a bit later. If you gain muscular strength. Anything those stronger muscles do becomes easier. if that is the case then more must be better. Well, that is typical muscle-head thinking. If some is good, more is better.
We are building athletes for sports other than powerlifting, and olympic lifting. In that way there is a "strong enough" destination wherein the athlete is fully strengthened for the sport she or he plays. In other words the acquisition of additional strength translates to no improvement on the court or field. In fact the acquisition of additional strength is a detractor. It detracts from the time that could be better spent on doing sport specific training or even just recovering from training sessions. Once an athlete is strong enough for their sport, they need only maintain their strength. One workout every 7 days or so will accomplish that.
For the athlete dysfunctional strength is, as I said before strength beyond what is needed. For the non athlete, dysfunctional strength is the pursuit of strength beyond which is healthy for the organism. There is the level of strength which allows one to merely do every day life. There is a level higher than that worth striving for that makes one more resilient to the demands of daily life and work Beyond that there is another level of strength that actually detracts from one's health.
Yes you may be able to lift a heavier weight to satisfy your ego, but at what cost? Higher blood pressure, unhealthy body mass, damaged joints. Remember, your heart works just as hard to haul 275 lbs of beef around just as it does 275lbs of lard. Just because you carry a low level of bodyfat does not mean you are healthy.
If you want to be a healthy adult and grow old, strong, and fit, you should emulate Clarence Bass, not some power-lifter or strongman competitor. Clarence is a model of health. The others are a cardiac event waiting to happen.