A perspective based on personal experience of output sharpening and stock and/or commissioned work:

When I've done pre-press work and sourced digital media for print any output sharpening carried out by contributor was a pain in the rear. The fundamental issue is that the contributor has no idea what the final output is going to be. The output sharpening required for a double page spread printed on uncoated stock using a four colour litho process is very different to what's required for a 1/8 page printed on coated stock using a digital press, clearly a low pixel count image for an online journal requires different treatment again.

Which is why, now that I'm on the other side of the fence, when I provide digital artwork or digitize physical media for pre-press or design work I offer a set of files of each image from small sharpened for screen jpegs up to full resolution tifs with no output sharpening. Some clients prefer to just receive a full resolution psd with very little processing, not much more than capture sharpening, levels/curves and colour; their layout artists/designers want to be able to make appropriate decisions depending on intended uses.

The important thing is to establish the needs of the client or agent and provide files that meet their requirements.

Of course a lot of the bulk carriers of stock images are primarily concerned with images principally for on screen use so such issues are of less significance.

Unfortunately in recent years I've dealt with an increasing number of buyers and even designers and printers who are oblivious to the specific requirements for different forms of reproduction. It can be difficult explaining why the large images look 'a bit fuzzy' or why you have left more space round the subject than they are used to seeing, however as image creators it's our job to educate and guide where we can. Alternatively for a small fee I will produce different versions of an image suitable for specific uses on demand. Though at the end of the day the client is paying the bill so if they insist on tightly cropped over saturated and over sharpened files in an inappropriate format with insufficient pixels then that's what they get, along with a polite smile and a warm handshake of course.

Cheers,
Ady