There's no question that a 4 or 5 inch utility knife is going to see a lot less use than your chef's knife or your paring knife, both of which have innumerable uses. The utility knife is a lot more specific, really being for cases where the paring knife is too short and the chef's knife is too heavy or thick. I have a 4" utility knife, which (of course) I got for free with a 6" Sabatier chef's knife. It gets used a couple times a week, for:
- scoring onions in order to mince them
- cutting limes in half (a chef's knife seems like overkill here)
- splitting small peppers
- slicing large California shallots
- cutting cheese
... and similar occasional, accessory uses.
Part of the problem with the 4" utility knife is that it's really a dwarf 6"-8" utility knife. The 6" or 8" utility knife, now commonly called a "vegetable knife", is far more useful; the long, thin blade is excellent for making paper-thin vegetable and fruit slices, and can be used as a fileting knife if you don't have one. At the 4" size, though, the utility knife is useful only for cutting things which happen to be small, and only if you don't already have a more general knife dirty.
If what you're really asking is "can I get rid of this knife?", the answer is "yes".
You can do anything with this knife that you would do with your santoku or Western-style chef's knife. These are real tools, and they are not especially delicate. It is certainly possible to chip the edge or tip (which requires an annoying amount of work to fix), if you drop the knife or, as the manufacturer warns, whack it against bones. This is a consequence of the relatively high hardness of your blade -- not of the fact that it's a gyuto -- but the flip side is that it should retain its edge very nicely for normal work. (A softer steel would end up with a rolled edge or dent rather than a chip.)
I guess that by "chopping" you mean quickly lifting and pushing the blade down through food so that it hits the cutting board. That's perfectly normal usage, and a plastic, wood, or rubber cutting board should not hurt your knife at all. (No glass! Do run it over a steel it often as you use it, though.) The foods you mentioned -- potatoes and fruit pits -- may seem hard, but they are much softer than the edge of your knife.
Best Answer
This will generally mean to not apply pressure (press the blade to the stone by either leaning/twisting the edge firmly into the stone, or keeping your fingers close to the edge) while you are in any edge leading phase of the sharpening motion. Edge leading and edge trailing abrasion have slightly different effects (regarding speed, burr formation, fineness of the edge), and so does sharpening at various levels of pressure (highly dependent on the stone used.).