Silicone Lubricant is essential to preserving the neoprene, latex or rubber gaskets around the neck and wrists of your dry suit to prevent them from cracking and or ripping from repeated use and exposure to the elements. During your my journeys, I spray the gaskets once per day. It is especially important if you don't have a chance to wash the dry suit in fresh water or if the water you have washed your dry suit is chlorinated. Remember that the gaskets on your dry suit will fail suddenly. One moment they are working, and they're not. So you have to keep them in good condition, from the day you buy your suit.
If the gaskets fail, you don't have a dry suit anymore.