I think that encounters should be meaningful.
You can have an encounter that is "difficult" WRT opposition stats and is not meaningful for the adventure, but just a stat block dumped there to provide a generic challenge, although out of the storyline: as a player I feel it boring.
I'm happy with encounters that are first of all meaningful for the storyline and important for the roleplay, and then if they are difficult under the technical (stat blok) point of view as well it is not an issue at all.
You can have an encounter that is "difficult" WRT opposition stats and is not meaningful for the adventure, but just a stat block dumped there to provide a generic challenge, although out of the storyline: as a player I feel it boring.
I'm happy with encounters that are first of all meaningful for the storyline and important for the roleplay, and then if they are difficult under the technical (stat blok) point of view as well it is not an issue at all.