at least the first times you play, before you know about them anyway . The blue dots makes it possible to find the first two hidden compartements in the pirates' boat, but if you jump off the boat it might be difficult to get out without perception. There are also a button in the dwarves' barrows, the exit in the watchtower, the elvish treasury room, a room in the white cliffs cave, the two levers in the Erathian sewers and several others. BTW do you think there is any difference between 10GM and 4E? I've only gone above expert once, and I didn't notice any improvement.

Then there is a rumour going around that perception reduces the damage taken from traps. I haven't checked it myself, it might be interesting if it's true.