Once a case reaches SCOTUS, the issues are no longer the specifics of the appellant's case but the general constitutional implications of the rulings when applied nationwide.
In the Presidential Immunity case, SCOTUS won't be looking specifically at President Trump's claim (they will be looking at the rulings by inferior courts on Trump's claim relevant to prior case precedent, defendants' rights, and constitutional interpretation), but SCOTUS will be more focused on the implications to future Presidents when determining the boundaries of Presidential immunity as it affects their ability to do the job.
SCOTUS will be looking at separation of powers issues, at Presidential immunity versus Congressional oversight, at Presidential immunity and the judiciary, at Presidential immunity versus impeachment powers, at Presidential immunity versus federal indictment, etc.
There's really not much for President Trump to do besides sit there stoically and sneer at the Justices.
-PJ
Thanks for the informative post, PJ!
Do you see no value for PDJT to be in the courtroom for such a case as this?
Optics alone demand it.