Today’s jails serve many different purposes. Other than holding suspects follow

They receive individuals pending arraignment and hold them awaiting trial, conviction, or sentencing.
They readmit probation, parole, and bail-bond violators and absconders.
They temporarily detain juveniles, inmates who are mentally ill, and others pending transfer to appropriate facilities.
They hold individuals for the military, for protective custody, for contempt, and for the courts as witnesses.
They release convicted inmates to the community upon completion of their sentence.
They transfer inmates to federal, state, or other authorities.
They house inmates for federal, state, or other authorities because of overcrowding in their facilities.
They operate community-based programs with day reporting, home detention, electronic monitoring, or other types of supervision.
They hold inmates sentenced to short terms (generally less than one year).