For example, if I'm part of a club and I think the treasurer is doing a bad job, if there are 'formal' elections I can run for treasurer (or vote for a different treasurer) and make changes.
In a structureless org it is much harder to tell the 'popular people' that, for example, some of the expenses they are having the club reimburse should actually be paid out of pocket (because by definition the 'popular people' have a lot of informal influence - average or unpopular people are much easier to correct).
If one person is highly charismatic they could wield huge amounts of power in a structureless organization - but in a structured organization there can be clear limits on what each role can do. Structures can constrain power and make it easier for those with less informal power to make changes or to create those limits.