رَأَيْتُ الْعُمَّالَ مُسْرِعِينَ.
I saw the workers while they were hurrying.
رَأَيْتُ الْعُمَّالَ الْمُسْرِعِينَ.
I saw the workers who were hurrying.
In the first expression, musriʿīna is an accusative circumstance describing the workers at the time of seeing them. In the second, al-musriʿīna is a definite attributive adjective modifying al-ʿummāla; it can help specify which workers are meant.
The shared lexical idea should not obscure the difference between a situation-bound circumstance and a noun's attribute. The speaker's purpose and the listener's question determine the most apt choice.