The basic biological phenomena rely on molecular interactions which are mostly non-covalent. When it comes to providing evidence that two molecules interact with each other, say e.g. two proteins that might communicate via binding to each other or a ligand and a receptor, an inhibitor and its target, etc. then we usually measure a dissociation constant. a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions.
The dissociation constant is commonly used to describe the affinity between a ligand (such as a drug or substrate) and a protein i.e. how tightly a ligand binds to a particular protein. Ligand-protein affinities are influenced by non-covalent intermolecular interactions between the two molecules such as hydrogen bonding, electrostatic and hydrophobic interactions and Van der Walls forces.
Reading manuscripts and published papers, there are cases where binding is used as an argument or proof, but often completely neglecting the underlying dissociation constant. E.g., when it comes to protein-protein interactions proteins are over-expressed and then co-immunoprecipitated, often without any control over the copy numbers of these proteins. Since binding is a function of concentration, anything will bind to anything when the concentration is high enough. The other case is that apparently specific inhibitors are used at such high concentrations (exceeding the dissociation constant originally measured) to prove that a phenomenon is mediated via a particular pathway or receptor. It is surprising how little concentration is taken into account! If you want to see what you want to see it does not seem to be a crime to rise the inhibitor concentration such that you finally see it. In order words, you have 50% chance that your inhibitor blocks your pathway and by rising its concentration, the chance will increase. To my opinion, many small organic molecules will inhibit a protein when its concentration is high enough. That is exactly why we need nanomolar inhibitors and also apply them at nanomolar conentrations.