Harry had deliberately left the trial of the Keepers until last, hoping for an emptier stadium and less pressure on all concerned. However, all the rejected players and a number of people who had come down to watch after a lengthy breakfast had joined the crowd by now, so that it was larger than ever.
Harry Potter and the Half-blood Prince
I think 'all' here refers to those candidates who attended the tryout for the Keeper, but I have no confidence about it. How should we understand the phrase "less pressure on all concerned"?