The random encounter has garnered much discussion over the years. It has been labeled as a trope from the D&D era that many have scoffed at. All of us can remember a time when the GM rolled the dice while the party slept. A few seconds pass and some wolf or goblin wanders into the camp. The party would be forced to dispatch the beastie before going back to sleep. It was a time of tables then and D&D had no shortage of them.
The definition of a random encounter is, an encounter that is not planned during the adventure. The GM rolls the dice and consults a table or just opens a monster book to a level appropriate page. The random encounter was seen as a bump, diversion or action filler for the adventure. Most players that I was acquainted with saw them as filler with no relevance to the story. This was one of the game mechanics that went out the window with encumbrance (another story) in our youth.
The adventure needs story driven NPC’s and monsters. The planned encounter is most certainly the best way to help the story. This is true regardless of the type of adventure being run, whether it is a sandbox, railroad or something in between. As GM I have created encounters before and placed them at appropriate times during the adventure. The appropriate time is when the GM feels that the story dictates their use. I have used them when the players have become complacent or arrogant. These reasons are dictated by the players not the characters. I add the encounter when it suits the story best or maybe to get the players going in a specific direction. With this planned encounter I have more control over the GM side of the story.
With encounters it is best to plan out the NPC. It does not have to be time consuming. The NPC just has to have the minimum stats and background to interact on a basic level. If the GM has this ready to go there is no lapse in game time and the story telling is seamless. This is certainly something that the players should thank you for.