Many times I see the imperfect when I would use the aorist. Here is an example:
αὐτὰρ ὁ ἐκ ποταμοῦ χρόα νίζετο δῖος Ὀδυσσεύς
ἅλμην, ἥ οἱ νῶτα καὶ εὐρέας ἄμπεχεν ὤμους·
ἐκκεφαλῆς δ´ ἔσμηχεν ἁλὸς χνόον ἀτρυγέτοιο.
Then he changes to the aorist again. I should understand it as a vivid description of ...