زَيْدٌ يُسَاعِدُ الْفُقَرَاءَ.
Zayd helps the poor.
زَيْدٌ مُحْسِنٌ.
Zayd is a beneficent person.
The imperfect verb foregrounds an activity; the nominal predicate attributes a quality. Classical analysis often associates nominal expression with relative stability and verbal expression with event or renewal, but neither construction mechanically proves uninterrupted permanence or a single occurrence.
Choose the form according to the intended predication and contextual evidence about duration, repetition, or character.