This reply will be different for everyone. The best way to tell if it's worth it for you is to sleep a full night on your pad without a pillow, and then a full night with one, and see how you feel in the morning.
As others have said, application also matters. If you are car camping, definitely use a pillow because the weight simply doesn't matter and it's way more comfortable. If you are backpacking, think about the level of comfort you want/need. Particularly if a pillow will allow you to be more refreshed for your next day and boost your morale, it's a very small weight penalty to pay.
As for my own experience, I used to go often without a pillow, and would either use rolled up clothing or nothing at all. But the refinement of my clothing system for backpacking meant that I no longer had a bunch of excess clothing to roll up. The weight and packed size of an inflatable pillow, especially this one, was so negligible and has made my experience so much more comfortable I personally consider it worth it.