Usually domain parking brings only a very low amount of money every month. If you are lucky, this amount may cover the registration fee, but this is not always the case.
You then have a decision to make:
- drop the domain because it has no interest and costs too much
- find a buyer in a reasonable timeframe
- develop the domain
This last option is the best one, as a developped domain is always worth a lot more than a domain name on its own. Obviously it also helps you prove the value of the domain and the amount of traffic it can get.
For more money, developping the domain is always the best option.