It is true that you don't need exact numbers and a rough extimate works quite well.
However that is even more reason to go for bell-shaped resolution distributions. Because with those you can plan around likely results being roughly in the middle and extreme cases being rare, so the average already gives you a good idea what to expect.
Furthermore the main disadvantage of the bell shaped resolutions is that some people find those to complicated to calculate in the head, but if you don't need the excat numbers, that drwback disappears.