As a prosecutor in the DA's office, there may be several different divisions you could be assigned to. For example, some prosecutors work on felony cases, others on misdemeanors. Additionally, there could be special courts - some places have "Veteran's Courts" where they try to help vets get back on their feet.
The head of the overall operation is the District Attorney. It is often an elected position. Therefore, there is a concern about being "too soft" on crime and how that will affect re-election chances. The DA will set policy. For example, he/she may say that it is a waste of resources (time and money) to prosecute possession of marijuana cases. Regardless what your personal opinion is, you will adhere to his/her wishes.
Prosecutors prosecute. While it is nice to want to help people out, it's all a matter of perspective. For example, someone I know was caught in possession of cocaine. He had to pay a lot of money in attorney and court fees, but, stayed out of prison. He had to attend counselling classes, report to probation weekly, get drug tested all the time, etc. It cost him a LOT of money. But, he learned his lesson. So, yes, he was helped. A lot of people facing criminal charges don't have money. Then what do you do? How do you give someone a break when they can't afford it? I don't have the answer to that.
Another thing prosecutors do is settle cases. There is lots of negotiating. Very few cases actually go to trial. So, let's say someone is arrested for Burglary (felony). They might plea bargain it down to Criminal Trespass (misdemeanor), along with various fees/fines/ community service, etc. Or, they could put somebody on Deferred Adjudication. With that, after a certain amount of time with no other criminal problems, the charge is dismissed.
Misdemeanor cases: theft (below a certain value), simple assault, criminal trespass, DWI, public intoxication, fighting, marijuana (small quantities)
Felony cases: Aggravated assault, robbery, kidnapping, arson, DWI (3rd offense- Texas), Drugs, burglary, theft (high $$$), credit card abuse, domestic violence, weapons possession
A lot of attorneys get their start in the DA's office. It will allow you to learn how they operate. You may decide after that to go into criminal defense. Many others start out working for Legal Aid, where you help people with various sorts of cases other than just criminal: apartment evictions, for example. I suggest you research that a little bit, and see if it isn't something you'd rather be doing. Here is the link for New Mexico's Legal Aid.