Hmm Sorry but I have to say that IMHO that's very poor advice.
A digital photo in a camera is measured in pixels. Now whether you set dpi to 72 or 300 the pixel dimensions remain the same e.g let's say a typical 6mp is 2848 x 2136
at 72 dpi its 2848 x 2136
if you change the dpi without resampling its still 2848 x 2136
The image quality hasn't changed. The image is bit for bit identical
By changing the dpi to 300 without resampling, you can now print it at its natural size without any reprocessing or quality loss at all.
A 6mp pic of 2848 x 2136 can be printed at 9" x 7" .. unless it's for the front page it's unlikely you'd need bigger than that.
The same can't be said if however you print it out, then scan it back in you're introducing 2 stages of image degradation, noise increase, loss of dynamic range..