Not enough for you to notice. The advantage of pulling the optical drive is to give you a space to install another hard drive. Pulling it just for the sake of weight isn't going to yield much savings
You should delete as many files as possible, the accumulation will make your HDD weigh more. You'll notice about as much weight difference as removing the optical drive.
You should delete as many files as possible, the accumulation will make your HDD weigh more. You'll notice about as much weight difference as removing the optical drive.