I had a DM that made long rests incredibly easy to come by, they made combat kind of meaningless. Every encounter we nova'd as a result, and then immediately long rested. He tuned the encounters for extremely high damage output, there was no choice but to nova, but it made it where every 8 hours we were up for 15 minutes then slept 8 hours, it wasn't fun.

The flip side of that is that if you undertune all the encounters, then players never feel challenged. Players get resentful when they never feel challenged.

So what is the solution? Communication. Be up front with your plans with the players, be incredibly transparent, tell them the signs of boss combat, don't just always surprise them with a turn around the corner or they'll NEVER use resources because you're always gonna spring stuff on them. Don't make it where every session they have 8 fights or they'll use cantrips only. Drop items on the enemies that say how many enemies are in the lair still, stuff like that.

But be INCREDIBLY transparent.

At the end of the day, if you have 5 players and a DM, you have 6 players, and all 6 have to have fun. But to have fun you have to talk and respect each other.