Not first time offenders. The guidlines will be for everyone, even repeat offenders. Lets take drugs for example.
Police have an arrest warrent for your roomate. They come to your house and another roomate lets the cops in. While searching the house, the see you sitting in your room with pot in your hand, you invite them into your room, the walk in and see a shotgun on the floor of your closet, its unloaded, but a shotgun nevertheless. They arrest you, now you are facing a potential felony because you were in possession of drugs and a dangerous firearm. You have never had so much as speeding ticket.
Would you agree that in that setting, you are not a danger to society? Would you also agree that society would not benefit from you sitting in jail for several weeks/months while your case goes through the legal system?
These are the types of situations where guidlines setting low bail would help. If the judge feels like you are a danger, they will still have power to set a higher bail. However, now there will be language that no longer allows a judge to do so in his/her discretion, but rather, the judge must have a compelling reason to raise bail. Society is still safe.