I must admit, I've simply never got why dpi is discussed as much in relation to digital photography and why anyone would want to convert the dpi of a digital file.
The numbers only have any relevance when you come to print the image and then only as a rule of thumb as to the likely quality of the output and the biggest size you can expect a good print from - there are many other factors that have more bearing on the visual 'pleasingness' of the finished print.
As a very generalised rule of thumb, an image is likely to look at its best printed out if you have about 300 pixels per inch to print from in the digital file you've selected - that should be about the optimum concentration of detail on the paper. So if you had a digital image 2832 pixels wide you could reasonably expect a really great print at 9.44" wide - or an 8 x 10 print.
But there are far more factors at play in terms of contrast, dynamic range, sharpness, contrast etc. and you can print at very much less digital pixels - per - inch on paper and still get great prints, the image itself has far more impact on how good it looks as it pops out of the printer than any dpi.