IV hydralazine is popular in hospitals because it is old, familiar and easy to use. A recent post at Emergency Medicine PharmD serves as a reminder of the potential for adverse effects. Among the downsides are unpredictable pharmacokinetics (it can hang around much longer than expected in some patients) and pharmacodynamics (unexpected and poorly tolerated hypotension can occur), activation of the sympathetic nervous system and cerebral autoregulatory failure due to its vasodilating effects.
As stated in the post, hydralazine is contraindicated in many true hypertensive emergencies and is not the drug of choice for any of them. And if it's not a hypertensive emergency (severe asymptomatic hypertension with no target organ damage) one should question whether a parenteral antihypertensive of any kind is warranted.