What If planning and actual Schedule capacity

Hi,
i am trying to understand What-If scheduling, and i have an assumption here, who can confirm this to be true or not?
This is in short what i found:

-I did run Global scheduling in What If mode over night.
-We did not accept or removed the changes yet
-now i try to schedule a new job by hand, and it seems this job is only schedule in a time where there is capacity available in the actual schedule, and in the what-if schedule.

So if i want the schedule a new Job i need to accept or remove the what if scheduling first to have a clear / real view of the capacity in my schedule?

i would really appreciate any help!

Thanks,
Michel