Ian (namvet), your explanation couldn't have been better! [righton] I'm impressed and delighted that you got here first 'cause you did a waaaaaaay better job than I could have (would have) done! :} :}
Welcome
sal4gal!
You've asked a question that puzzles a lot of people who are 'grabbing' or even creating pictures for print purposes.

The thing to keep in mind, is that file size is 'relative' to output (print) resolution. The bigger the picture appears (pixel dimensions) at 72 ppi on your screen, the better! And, as namvet has shown you, by unchecking the 'resample box', you will be packing all that pixel information into a smaller print size, thereby raising the print quality/resolution.