Dungeon Traps, do they make sense?

In my time of playing OSR type games, and of course the original "Dragons & Dungeons" I think I must have read a thousand adventures. Its been starting to grind my gears a bit when I come across traps that make no sense.

For instance in my recent Basic Fantasy/Scarlet Heroes solo games I'm come across a trap that makes sense and one that didn't.

The first trap, the one that made sense was a pit trap that guarded the entrance to the dungeon. It made complete sense because if you knew there was a safe ledge on one side you could scoot past the trap. That makes sense because then the dungeon owner could go outside, and leave the dungeon protected, rather like having a key to a door. Furthermore the trap had an attached and hidden lever that could make the trap safe. Thus the dungeon owners could make it safe and transport goods on pony-back straight in over the sole entrance to the dungeon.

A similar but senseless trap was another pit trap that fully blocked the only entrance to a section of the dungeon. There was no secret side passage, nor was there any way to make it safe or reset it. That makes no sense. I mean, had the dungeon owner locked themselves in, or locked themselves out? 

Why would you lock yourself out of a dungeon? Are you a recovering alcoholic and put all the dwarf-beer on the other side? I suppose you might have found a nasty cthulhu-resurrection device and are trying to stop anyone finding it...but even then you'd be better off burying in rather than building a disguised pit.

Why would you lock yourself in? Are you entombing yourself? Beats me.

Dungeon traps need to make sense. Like the first example above they need to be resettable, re-useable, or bypass-able. Maintaining the "sense" of them makes the traps feel real to the players. Without it you run the risk of out-of-character moments while players try to work out what the heck its all about.

One other nonsense I can do without, is traps in the middle of a dungeon for no reason at all. There needs to be a reason for the trap, otherwise you might as well just randomly kill the characters without rhyme or reason. 

Please if you are including traps in your dungeon, spend some time thinking about how the denizens of the dungeon move around the trap, and why the heck it was there.