We actually had a pretty extensive thread about this recently, and the argument boils down to people having different opinions of how transparent mechanics should be to players, including things like DCs for proposed actions. I'm generally in the camp that the players discover those difficulties by trying it. The only certain information they possess is how good their character is at a thing.
This is off topic, though, so I think we should re-open that discussion in another thread.
If you have no context for the number,
you DON'T know how good your character is.
Without a
context for the numbers, +10 to a roll tells you nothing except that you're better at it than someone with a +5. If the DCs are regularly 30+, it makes essentially no difference whether your modifier is -1 or +11, your chances of success are abysmal and always will be. If DCs are typically around 10, having +10 is nice but maybe overkill while +5 is ample for most characters, unless the DM decides that you don't just need to pass one check, but four.
You can only make informed decisions about your abilities when you can actually
predict, up to the variance of the dice, what your likely results are. Hiding the entire procedure behind the "DM says" black box means that you cannot do that—and humans are really, really, really
awful at statistics, especially when they aren't carefully tracking successes and failures AND can't even in principle know what the actual range of success on any given roll might have been.
Edit: Also, reading comprehension failure, I did not see your final sentence. I will abide by this request, and apologize for not seeing it before writing a response.
