People who are using drugs sometimes often need various types of "paraphernalia" to accomplish their goals. This is something that they might not think much about, but it is something that can lead to criminal charges. It is possible to face criminal charges based solely on the presence of drug paraphernalia, even if there aren't any drugs present.
Some items are clearly used for drugs, which makes these a bit of an easier target for police officers to pick up on. These include things like roach clips, which really don't have any other purposes. In this case, the officer who finds the roach clip might initiate an immediate arrest and confiscate the clip.
There are also some items that can be used for legal or illegal purposes. In these cases, the circumstances surrounding the items will dictate how they are perceived. For example, a digital scale in the kitchen near chicken isn't unusual. The scale is legal and it is being used in a lawful purpose – to weigh food items.
If that same scale is on the living room table near plastic bags and razor blades, it might be assumed that the scale, which is legal, is being used for illegal purposes. At that point, the bags, razor blades and scale can all be classified as drug paraphernalia in a criminal case.
Some people falsely believe that drugs or drug residue have to be found on the items that are marked as drug paraphernalia. You can face this charge even without drugs or residue, but the fact that there isn't anything on the paraphernalia might be a point that you can use in your defense against the criminal charge.