I’m torn about them. On the one hand they free up the combat design to be as wildly different from the exploration as it wants. Which can result in really creative stuff. Favorite examples are Undertale, MegaMan Battle Network series, and Tales series.
But on the other they interrupt the flow of exploration, the music, you forget where you were by the end of combat and they can be very annoying if they happen to be common or just as you’re about to leave an area. The consolation prize of growing stronger with every battle only helps so much.
They’re not the worst thing ever, but I’m happy when a game finds another way to challenge the player that isn’t “throw an enemy encounter at the player every ten steps”.
Nowadays I particularly enjoy games where the encounter is fought on the map itself instead of having a transition screen and a separate map. Games like Sea of Stars, or Yakuza Kiwami for example. I find that removing the transition screen also removes much of the tedium I feel with enemy encounters in video games.