shannon - i think if you're doing a "natural FET" - where you O and then transfer after, you don't need the LP support as your ovary (and the corpus luteum) will produce the progesterone until the placenta takes over fully

if you're doing a "medicated FET" - where you have the HRT - the hormones are introduced and there is nothing being produced naturally - so you don't make the progesterone for yourself. in that case, you get the support

in some cases, FS makes it a matter of course that you need LP support - but a lot of people (like sushee) make enough P4 themselves and don't NEED it...

hope that helps to clear it up...