I definitely use random encounters, but they are from a list of various encounters I've already scripted and prepared. Depending on the game situation and player choices they might encounter some of these or none. It all depends on dice rolls for things such as Perception as well as decisions. Decisions are as simple as whether they choose the mountain pass or swamp to get to their destination. Random encounters would be planned for each so depending on where they chose to go these may occur. However, I know this is old school, but random encounters occur if a player rolls a certain number on a dice. The dice rolled can vary from a D4 to a D20 depending on how dangerous and populated that terrain area is. If the player matched my number on the same dice the random encounter happens. It's completely random, but players have fun rolling the dice and then seeing if an encounter happens due to their dice roll. Random encounters are not always harmful and are often favorable or fun role playing. Gotta have random encounters in a game or else things are too scripted.