How would the BCC chain know what coins you spend on the BTC chain and vise versa? Wouldn't their separation mean you could sell both 100 BTC and 100 BCC? After the split the two chains will not interact or connect at all and only share the historical block chain, so how would they know you spent 10 BTC or BCC to take i from your balance of the other?
I think you need to be more clear with your advise. It's not "don't sell your BCC", it's "don't sell". Everyone (with private keys) will get an amount of BCC that equals the amount they have in BTC. For example, let's say someone owns 100 Bitcoin. They will then also own 100 BCC. If they sell 10 bitcoin, they will then have 90 bitcoin and 90 BCC.
The more I read posts today the more it sounds like people think they're getting something for free. They're not...they're just getting the option to convert existing Bitcoin to Bitcoin Cash.
Yes, he HabBear has no idea how it works.
Once the fork is complete you will be able to move your private key to a wallet that supports BCC and be able to spend your BCC. If you spend BCC, your BTC will remain, so you ARE getting something for free!