As a volunteer who visits the jail on almost a weekly basis, I can verify that there are plenty of prisoners serving time. Actually, the United States holds a record number of inmates in prison, compared to other countries.
This costs the taxpayers money, and sometimes may be counter-productive in reducing crime.
For instance, a person serving a jail sentence may lose his job and be unable to pay fines and make restitution. His support network in the community may be damaged. The result is a person who has less to live for after release from jail, and fewer resources to help him make good choices. On the other hand, a person who is serving probation has to demonstrate that he has learned his lesson, will make better choices, and will not repeat the crime, all with minimal cost to the taxpayer.
Does this sometimes result in repeated crimes, eventually resulting in prison sentences? Of course. Does it result in people making a mistake, and then going on to become productive citizens who pay taxes? Again, the answer is affirmative. If we were all imprisoned for minor offenses, who would be left to run the correctional system?