That is true, to an extent, but experience is usually the better choice, IMO. If experience isn't an option, or you get some randomly generated loot anyway, then sometimes a good piece of equipment now would help more than a bunch of better equipment later.
In D2:ED some people also waited until they cleared Broken Valley before opening any locked chests, so the random loot was better, but by then do you really need that much loot?
I just open locked chests as I come to them. The equipment you find in them as you go really helps. Or you could always just sell it
