First I must correct a statement made earlier - Benzos do not bind calcium channels, they bind to an allosteric site on GABA-a subtype receptors at the benzodiazipine site, causing an increased sensitivity to GABA (potentiation) that allows the CHLORIDE ion channel to open more frequently (not constitutively active like a barbiturate) and that's why the OD death risk is low, if not impossible on a monodrug overdose. Opiate users often like them because both opiates and GABAergics are inhibitory chemicals. Opiate receptors cause downstream depolarization on nociceptive neurons in the brain, and in the gut and elsewhere, making the neurons less likely to fire and allowing cholride ions to more freely cross cell membranes. Basically they blunt unpleasant feelings, like nausea and itching, and more commonly, withdrawal symptoms.
I personally became addicted to them because my anxiety and depression succumbed to the effects of benzos allowing me to get things done while in withdrawal. Eventually, though, after taking too much I have done some regretable things due to benzos (while on them), more so then from doing things while off opiates to get money to get high.