Seems to be some confusion as to what CROP means. What I want to do is actaully cut out a part of the frame, and have the resulting video change dimensions to match the cropped area. All premiere does when you use the crop effect is to drag a black bar onto the frame, but the video dimensions stay the same.
To be very clear, crop a photo in Adobe Photoshop. The resulting image now has completely different dimensions. Also, Adobe Express on the web makes cropping a video incredibly simple, and it does exactly what you'd expect a CROP to do.
You would need to create a sequence at your chosen dimensions and then edit your clip into it. Or with your clip already on the sequence, go to 'Sequence Settings' and then change the frame size. You might have to do this several times to hone in on the exact size you want, whilst moving the clip if the area you want isn't in the middle of the frame.
I don't believe there is a way to just crop the frame on the fly, like you would in Photoshop.
Though incidently, you can do this in After Effects using the region of interest and then 'Crop Comp to region of interest'.
Are you cropping lots of videos to different dimensions?