You are legally allowed to represent yourself at any stage in the criminal justice system. Although you can represent yourself it is usually not a good idea. Unless you know the law and how the system works representing yourself can be extremely detrimental to the final resolution of your case. For instance, in DUI cases you need to know not only the law regarding DUI offenses and defenses, but you should also know how to challenge field sobriety tests and the chemical tests. In addition to this, you need to understand all of the possible alternative sentencing options you may qualify for so you can negotiate the best possible plea deal if you decide to plead guilty.
Hiring a competent and experienced legal team is worth the expense as it is the best way to protect yourself and make sure you get the best possible outcome for your circumstances.