DPI Dillema

My understanding of DPI for printing an image is that you pick the desired resolution, and then calculate the pixel-size from that. For example, Epson printers native resolution is 360 dpi. Thus if I want to print an image at 5" x 7" it will be 1800 pixels x 2520 pixels at 360 dpi. Photoshop handles this nicely.

When I save this image from Photoshop as a tif,it comes out at about 85mb.

Interestingly, I can print the image from Lightroom, set the desired print resolution and print size, and it all works from the 8 mb RAW file!

So - my question is, is there any advantage in creating the large tif file, or is that just a side-effect/cost of working in Photoshop? Does Lightroom 'automagically' create the equivlant of that big tif file when it sends the RAW image to the printer?

=Alan R.