Being arrested can be a very frightening process for anyone, but the process usually isn't over once the handcuffs come off. There is a hearing or meeting with prosecutors and attorneys to determine your guilt or innocence. No matter the arrest and no matter the charge, note when it's good to consult with an attorney.
1. If there is any possibility you'll be facing jail.
Don't assume that you can or should just face your jail time and get it over with; even a few days in a county or city lockup can be very unpleasant if not downright traumatic. You would also need to consider how that would look on your permanent record, who would take care of your children and home during that time, and so on. Jail time can often be negotiated with prosecutors and attorneys so that you avoid this sentence, but don't assume you can just talk the courts yourself. Some crimes have minimum jail times associated with them, and you may not know how to negotiate the charges themselves. A skilled defense attorney can help you to avoid jail altogether or get the sentence reduced as much as possible.
2. If this isn't your first offense.
First offenders aren't always given leniency by the courts, and even more so those that have been arrested before. If this isn't your first offense, you may see that the judge and prosecutors will give you maximum punishments and fines, just to "make an example" out of you. This can make an arrest for even a relatively minor offense into a very serious situation for you, so it's best to have an attorney work with you if you're a repeat offender to ensure you get as much leniency as possible. They can also try to negotiate the charges to lesser offense so that your permanent record is protected.
3. If you know your criminal record will greatly affect you.
A criminal record of any sort is usually a problem for just about anyone, but even more so for those whose jobs may be directly affected by their arrest. For example, if you drive a taxi for a living, a drunk driving arrest will probably affect you more than someone who works in a fast food restaurant. If your arrest will have great impact on your personal life and especially on your livelihood, have an attorney negotiate the charges and your record as much as possible.