Always listen to what the photographer tells you. But, if you are really uncomfortable with a pose, POLITELY let your photographer know how you feel, a truly great photographer will listen. Remember, if your photographer is a trained professional, and he/she will not appreciate "UGH, this feels dumb" or "Eew, I hate that" comments. Negativity will show up in your images and will come back to haunt you when it's time to order your images... Believe me, photographers will not budge an inch on prices or give "extra perks" when it's time to sit down at the bargaining table and your senior has been less than pleasant to work with. Besides, a professional photographer will know what looks good and what doesn't, but they should be receptive to your ideas, too.