Writing a check for cash can be done two ways. A person can either write the word "cash" in the "Pay to the order of" blank line on a check or put his own name in that payee space.
Writing a check with "cash" in the payee line is an easy way to pay a bill when it's not certain the exact name or person to whom the check should be payable. However, a check written to cash needs to be handled with care because it's exactly like currency. If the check is lost or stolen before it gets to its intended party, there's no way to stop someone else from depositing it. The check holder's account may incur a fraudulent transaction. This is one reason some banks refuse to honor checks written to cash and why other banks may place extra holds on the funds.
Another disadvantage of writing checks to cash is that it is harder to keep track of finances. When payees are clearly indicated, it is obvious where the money is going. With "cash" or checks written to oneself, it's easy to forget exactly where the funds went or for what purpose.
One good thing about receiving checks written to cash is that they're usually easy to cash at the banks on which they're drawn. Otherwise, they can be deposited by endorsing the back with one's name and account number.