What are the disadvantages of using concealer only without foundation?

I've never used make up before, and I just bought concealer without anything else - in hopes to cover up my acne & blemishes & scars. I didn't buy anything else, eg. foundation because it's my first time buying make up and I don't wanna get too much. I also want to go for a natural, no make up look. Is there anything wrong with just using only concealer and nothing else? Would my skin look patchy or anything?
What are the disadvantages of using concealer only without foundation?
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