In what situations are flexible joints particularly useful?

Flexible joints are particularly useful at river crossings due to the dynamic nature of the environment. Rivers can experience fluctuations in water levels, currents, and flow conditions, which can lead to shifts in the surrounding earth and up to considerable stress on pipelines. The flexibility offered by these joints allows for movement without causing damage to the pipeline or risking leaks, which is critical in maintaining the integrity of utilities crossing significant bodies of water.

In contrast, while flexible joints may also be applicable in underground installations, their primary purpose at river crossings is to accommodate the unique stressors associated with waterway environments. Similarly, they are beneficial when dealing with abrupt temperature changes or in residential plumbing, but again, those scenarios do not encompass the same level of environmental stress faced at river crossings, making this answer the most relevant in this context.