I have never had an LLC so I can't speak to the details of the legalities. That said:
There's little value in setting up a "business" bank account if you're going to also use it for personal expenses. The whole point of a business bank account is to separate your personal finances from the business finances. If you use the business account for personal spending, you've destroyed this idea.
The idea is supposed to be that you can show an auditor your bank statements and say, See, here is all the money coming into the business and going out. You should be able to reconcile your accounting system with your bank account. There should be a 1:1 correspondence between transactions. If you are audited by the tax man, you have a paper trail from the bank to back up your records. That doesn't prove you're not lying on your taxes, of course, but consistency is evidence of good faith.
But if you mix in personal spending, then all this goes out the window. Now some transactions on the bank statement correspond to business transactions and some don't. The balance on the statement has no relationship at all to how much cash the business has.
If you're going to do this, why even bother to set up a business account? Rather than create a "business" account and sometimes use it for personal expenses, why not just use your personal account for business expenses?
Assuming that you insist on doing this anyway for whatever reason, yes, you should absolutely document personal transactions. If you don't, then how do you know whether any given transaction is business or personal? If it's not recorded in your business accounts, does that mean it must be personal? Or could it mean that you simply forgot to enter it into the accounting system? You'd then be reduced to trying to remember what each transaction was. At which point, why bother having an accounting system at all? Why not just rely on your memory and guessing?
As I said, I've never operated an LLC, but I would GUESS, just thinking logically, that you would seriously endanger your limited liability status by doing this. How would a court or auditor know if the business could afford to pay a bill or a judgement, if the balance in its bank account is partly business funds and partly personal funds? For you to go to court and say, Well I have these other records that show that only $X of that is the business's money, and I'm pretty sure that this deposit was personal money, I don't have any proof of that or even any records to back it up, but I think I recall that when I made that deposit 5 years ago that that was personal money, probably.