illustrator - create pdf compatable file

[EmerginT]

Hi - whenever i do an illustrator file - I save one copy as an .ai and then convert type to outlines and save another file as a pdf for the customer to proof.
But when you save as an .ai file - that box comes up with a checkmark that says "create pdf compatable file" . So is there already a pdf file somewhere and am i taking an extra step by making a pdf file?
Also the box says something about subset fonts and you can change the percentage rate.
What does this stuff mean?

[Mynock]

I believe that just so other programs like Photo can have a preview of the file.

[jimking]

Ditto, Mynock

[Mynock]

Ditto, MynockIt's nice to hear that I actually know what I'm talking about from time to time.

[Sonic_Nerdish]

What they said about PDF compatible file.

Subsetting the font means that it only includes the actual characters that are used in the file, which keeps the file size smaller. I believe this also helps prevent problems due to font licensing restrictions. If you are changing type to outlines, it is irrelevant.