Once you see video of babies flying around the airplane cabin during turbulence, it's hard not to get them their own seat. It's pretty much impossible to hold onto your child during a quick/sudden drop, even if 99% of flights dont' have that happen.
That said, I always got my daughter her own seat for comfort reasons and I'm glad I did. It made my life soooooo much easier and I have to admit that if I had a magic wand and could completely do away with all physical dangers, I'd still get her that seat. Just don't overburden yourself bringing things along - bring the carseat and a backpack with toys, diapers, a book for you, food, etc. It's very easy to pack 8 times what you need - remember that you have to drag it all through the airport itself, not just stow it on the plane....... and may have to drag it all while also carrying the baby. (I found that a backpack that went on both shoulders was easier to manage than a diaper bag that only had the one strap.)
Enjoy!