No just that you don't want to be having some days in ketosis and other days along way from ketosis. So you need to aim to eat about the same number of carbs each day. Being in ketosis is one way to know you have your carbs lows enough, but a lot of people can control diabetes without getting down to these levels.
The real risk is that if you reduce the amount of food you eat without greatly reducing the proportion of carbs your body will tell you to eat a lot more, and slow down.
I think you need to be in ketosis for many hours a day so as to remove fat from your liver etc, this can be done by skipping breakfast and lunch for example if you have a high carb dinner. But any reduction in carbs will lower BG even if you don't burn of fat.
