The advantage of making the distinction is you can discuss the subtly different semantics which often arise in the area of parallel, concurrent and distributed

The advantage of making the distinction is you can discuss the subtly different semantics which often arise in the area of parallel, concurrent and distributed computing. If you equate them, you can only discuss with limited level of detail, which makes it harder to understand the subtle differences coming from different computational models. For instance, the subtle difference arising from MIMD execution and SIMD execution. The former allows for concurrent execution, whereas the latter does not. However, both are parallel execution models. This isn't theoretical either as GPUs are strictly SIMD machines in their execution.