Here is something I stumbled upon with a client this week.  Let say you have a situation like this:

Customer sends a check for $4,750.00

This is going to be applied to 5 invoices each for $1,000.00

Customer decides to only pay $950.00 on each invoice because the feel they are owed a discount.

You agree and go to the cash receipts entry screen.

You initially enter $5,000 as the check amount and then click on these 5 invoices and write off $50 on each one. You then go back and try to change the $5,000 to $4,750. GP will not let you as it says you cannot change the amount to already applied documents. Now you physically have a check for only $4,750 and this is what needs to appear on the bank deposit.

Now if you had originally entered $4,750.00 on the cash receipts entry screen and did the same thing, GP very happily allows you to click Save and post.

This all happened because the user wanted to use the amount as a checksum to see that the invoices paid equaled the check sent. So they entered a  bogus number and just kept clicking on the apply window until all the invoices were paid.