In my subfield of computer science I observe that workshop papers often are not thoroughly reviewed. It even appears (attention, possibly controversial assumption incoming) that workshop-paper acceptances are used to increase the number of participants at the conference, because authors of accepted workshop papers are required to register for the conference. Moreover, workshop organizers are often desparate to get enough submissions in order not to be forced to cancel the workshop. Hence, they are happy to accept submissions even if they do not completely fulfil certain quality standards.
Speaking about the quality of the papers, they often do not contain rigorous evaluations, hence, the presented results possibly are not really reliable (please note, that, of course, there are many terrific workshop papers out there!). I have a feeling that these papers would not get accepted at a (good) conference due to lack of maturity etc. I am aware that (especially in computer science) the publication path is often like this: early/initial work in progress is submitted to a workshop → if the work gets more mature it is sent to conferences → after some more work it is probably sent to a journal.
My question is: Given the above circumstances, should workshop papers be cited?
Since the quality (hence, the results) of such papers is often lacking, I ask myself whether it's a good idea to make a reference to it. One further thought is that references are often used to show that something has already been done or addressed. Therefore, the reference is used to argue that the problem addressed by the workshop paper should not be addressed anymore which is probably a wrong assumption if we assume that the work done in the workshop paper is sub-par.