Here is my take on it, but this is just my best guess, and does not reflect anything that I have read anywhere about this.
We never needed to use adjuvants before. Many doses of seasonal flu go unused because most people do not get vaccinated.
We now have a completely new situation. This is a novel flu virus, and there are many possible naive hosts globally. If the decision is made to go forward, and produce a vaccine, it will be in limited quantities, certainly not enough for everyone on the planet.
The link below describes an expermental vaccine made for one of the bird flu viruses, H9N2 that infected some children in Hong Kong in 1992. Like H5N1, bird flu, H9N2 is a virus with pandemic potential as it is another novel virus, and we would again be the possible naive hosts if infected.
As explained in the commentary, the seasonal flu vaccine contains 15 micrograms each of three different circulating flu strains of our seasonal influenzas-- much higher than the 3.75 micrograms of H9N2 flu virus contained in the lowest dose vaccine tested in this trial. It had been thought that protecting naive hosts to a novel virus might require two vaccinations. That is where the adjuvant comes in. Adjuvants increase immune response, and may dispense with the need for a second injection. As you can see in this trial, they were able to use much less than has been standard for each flu contained in your regular flu vax.