Although they need to be the same layer.
Two identical layers are likely to be as big as two different ones, assuming the same colours.
( Pedantichrist http://lordmanley.co.uk/gas/, Sun 10 Feb 2008, 20:11, archived)

How strange.

( my other username is a porsche , posting shit pictures so you don't have to, Sun 10 Feb 2008, 20:15, archived)

in the resulting GIF you only have one layer per frame.
any decent gif animation package should optimize that no matter how things were arranged in the source files.

worst case scenario, assuming your gif writing software doesn't work like that: just run the gif through GIMP's "optimize for gif" or gifsicle or something like that.
( but the hedgehog can never be buggered at all is drinking bloody maries, Sun 10 Feb 2008, 20:22, archived)

this is all
unusually constructive, peeps. cheers
(the_whore_of_mensa You like it so much, I make it a part of you!, Sun 10 Feb 2008, 20:25, archived)

in the gif,
when saved, all the stuff that remains the same per frame is discarded after the first frame that uses it.
( Pasanonic WARNING - May induce flouncing., Sun 10 Feb 2008, 20:25, archived)

Indeed,
but I find that images which are the same do not optimise as well as if you delete all the same bits from the subsequent layers and have a transparency through to the base layer.

I am not wording this well, bear with me.
( Pedantichrist http://lordmanley.co.uk/gas/, Sun 10 Feb 2008, 20:29, archived)

IF the resulting pixels are exactly the same, it shouldn't matter
but when you're working with many "same" layers it's pretty easy to much up somewhere and I do sometimes do what you're describing here (I think) to make it easier on myself.
( but the hedgehog can never be buggered at all is drinking bloody maries, Sun 10 Feb 2008, 20:39, archived)

Yes, I have experimented with two versions of this:


I was wrong.
( Pedantichrist http://lordmanley.co.uk/gas/, Sun 10 Feb 2008, 21:22, archived)