Depends if you have any muslin blankets. If you have them, you could do without cellular for when you take the baby out
I had one for my last and didn’t really use it. But be careful with sleep bags as a lot of the time newborns are too small to use them. I had a 4kg baby with my first and she was ok from the start but friends had to use cellular blankets until their babies reached the minimum size for the sleep bags.
Sleeping bags are often too big for newborns so a blanket is a great option for first bedding.
Yep can be handy for during the day naps in the Moses basket/pram and in the car seat that you can’t use a sleep bag for