Writing a check to cash means writing "Cash" on the payee line. The primary reason people write a check to cash is to make it easy to deposit or cash out at a bank. There are risks to filling out a check this way, though.
Sometimes, people write a check to cash as a means of getting money out of their own checking account. This tactic isn't as common as of Feb. 2015, since most people have debit cards for their bank accounts. However, you make write a convenience check on a credit account to cash to get a cash advance. One of the main reasons people write a check to cash is because they don't know the name of the payee. When a check is written to cash, whoever receives it is able to make the deposit or use it to collect the money.
Cash Payee Risks
The risk of making a check out to cash is that whoever possesses the check can use it. Therefore, if the check is lost between when you write and when the intended person receives it, you must by a stop payment on the check to avoid the finder cashing it. A check made out to cash may also allow for check fraud or misuse. An individual working for a business or nonprofit might take the check and use it personally.