If you need imaging for pneumonia / consolidation it’s definitely better to X-ray (very accessible), you may get lucky and see a peripheral pneumonia if it’s dense enough but the negative predictive value isn’t there as you have very little depth of penetration.

Pulmonary edema is presently still X-ray preferred as it’s easier to compare cardiomegaly and pulmonary vasculature with priors, as opposed to US images which are operator dependent and likely not saved. There is increasing research on cardiac/caval measurements as surrogates for CHF but the standard measurements haven’t been fully developed to be clinically ready as the sole investigation, I expect one day in the not too distant future this will change.

Pleural effusions go either way, as an initial investigation you’ll usually still want the X-ray to evaluate for parenchymal disease and CHF so why do two tests. With that said we drain effusions under US guidance so if that’s your only clinical question for sure POCUS is great, I would say that’s an uncommon scenario though unless the patient is known for chronic/malignant effusions and you may only be assessing for reaccumulation and planning drainage.

Pneumothoraces on US still need X-ray confirmation and to accurately assess size as the sliding sign isn’t that reliable yet.

Given how broad most differentials are for dyspnea it’s hard to find a patient where US (either in radiology or POCUS) is satisfactory as a single investigation when concerned about lung/pleural disease. It’s awesome for cardiac stuff like wall motion abnormalities and gross dilatation/dysfunction in the acute setting, but you’ll still want a formal echo for accurate size measurements. At my institution we still have echocardiographers on backup call for the cardiology fellows, although they’re being called in less and less.

Abdominal imaging is way more of a crapshoot. Acutely presenting patients are often unwell, have large body habitus, and acquiring adequate images is hard even for us. If you’re in a place without emergent/urgent US access it’s certainly better than nothing. You would certainly never diagnose malignancy or workup a mass based on POCUS, this can be really hard even for radiologists + sonographers.

Personally, I hope clinician skills reach the point where I don’t do (or do significantly less) acute US studies so this isn’t gatekeeping at all. I would gladly give up the work. A lot of the issues stem from how POCUS was implemented, currently it is very unstandardized and you can get certified after a weekend course in some places and are being taught by other clinicians. It would be better if they rotated with our sonographers to learn the skills in my opinion.

Edit: I don’t disagree re: stethoscope but it’s already been replaced by X-ray in any facility with one (which is most places), chest imaging is a bad example of where POCUS will be useful for the above reasons. Increased skills at biliary, renal and testicular pathology as well as echo are way better examples and instances where stethoscopes are already outdated. When I was an intern 5 years ago we had already moved past auscultating murmurs, which are generally not acute, and you would still get a formal outpatient echo for accurate measurements (these take a while and you need to be really good at measuring, slight obliquely can significantly alter values).