First, it depends on the judge in whose court the case falls. Some judges give p.r. bonds more often than others. (They are a rarity in Harris County.) It also depends on prior criminal history - one generally should have a limited history and no violent crimes in the past. The current charge is generally not for a violent offense. The person must be connected to the community - they must be able to verify an address and relatives or friends, employers, etc.
The purpose of a bond is to assure that the accused appears in court. A p.r. bond allows the person to be released without posting money to assure that appearance.