I ran Out of the Abyss recently, and the module uses a lot of random encounters. In the beginning, i just rolled the random encounter table during the session, it ended up being mostly described as 'You bump into X number of Y monsters, roll initiative.'
IMO they could work if the DM was good at improvisation and making things up on the fly. I later pre-roll, or even personally pick on the encounter table and give it more thought on why they are there, what are their motives and also their tactics and loot. Also, i didnt like that random encounter could roll out really unthreatening encounters like a small band of 4 orcs or something. Seems like a waste of time. I would spice it up by adding mounted orc raiders on Aurochs, orc spell casters and some grunts.