Infant car seat option for stroller??

FTM due early Feb. After much research I purchased a Cybex gazelle stroller with bassinet (I really wanted the bassinet feature for various reasons). I was planning to also purchase the car seat adapter for the car seat I already have (Chicco keyfit). However, now I’m wondering how necessary that configuration really is. I can’t really think of a situation that I would really NEED to keep baby in the car seat rather than transfer to bassinet. If baby is asleep and I am going to run a quick errand, I could just place the car seat in the store cart, right? Is there a situation I’m missing? TIA!