Just remember one thing - whether it is 1st, or 4th, or 189th chair - whoever wrote the music and the arrangement did put in so many instrument because he/she/it thought they were necessary. Take away even the tiniest bit, and the music is incomplete. No instrument and no chair is more important than any other. It may be that some instruments and some chairs can be heard better by the audience; but every single part is necessary. When some composer guy (I forget which, but might have been Beethoven) played before the Emperor Napoleon Bonaparte, the Emperor (who liked simple airs) after the concert told him: "You've written very many notes there." he got the reply "Exactly as many as necessary, Sire." That's the spirit.