I always find it kind of irritating if I type a correct command that fails for whatever reason I am presented with a giant block of text of the help where only some where at the top the real issue is listed. If I get the help displayed I somehow immediately think I used some wrong --parameter or command.

However in cases like:

• running qbs in the wrong directory:
  ERROR: No project file given and none found in current directory.
  Is pretty self explaining and would not need a spammy help display and
  thus scrolling up to see the issue
• having multiple project files in a directory:
  only ERROR: More than one project file found in directory '...'.
  is printed. No more help --> I can directly see the issue without
  scrolling

So it seems to be done this way in some cases already. But I think it would be most intuitive to do it this way everywhere but for the "Invalid use of command" errors (where the chance that you will actually need the help is given).

Regards,
Erik