Time trial frames: Extended Seat Tubes benefits?

[fiks]

I though was to save weight because a thin walled steel tube is lighter than a thick walled alloy seatpin.

I think sizing a lo-pro is a bit more flexible compared with the standard horizontal top tube road frame. Seat tube length is not important anymore, whether extended or not, since it doesn't relate to the top tube length.

Instead you need to look at the top tube and head tube lengths so you can position the bars at the correct position in relation to the saddle and BB.