[ramparrt]

It's not really very useful. Most serious but recreational cyclists are limited in terms of available training time and recovery. When faced with the option of spending their limited time on the bike or in the weight room with the objective of going faster, the bike is almost invariably the right answer. The reason for that is that watts/kg and watts/cda are the 2 basic determinants of how quickly a cyclist can get anywhere. Weight lifting will increase the watts but only on a very, very short time scale (ie, sprinting). Weights will increase the kg and cda for cyclists who eat in surplus. Thus, the cyclist will be no faster and most probably actually get slower.

The obvious exception to this is track and road sprinters who benefit considerably from doing weight work. Everyone else serious about riding should just ride.

[nikofeyn]

there is hardly a sport where strength training and conditioning is not useful.

[ramparrt]

That is a true statement, however when the objective is getting from point A to point B and those 2 points are >1km apart strength is rarely a limiting factor for cyclists. Available training time and recovery rate are however. Many of the benefits of gym based strength training can be achieved on the bike by performing on bike sprints all the while maintaining specificity. The modern, generally accepted principle is that weight training for cyclists is not the best use of training time.