I was looking for a picture of a 914 fuel tank to help me put mine back together after painting it.

While looking on google images i found a picture of a tank installed in the car but without the expansion fitted. I know this may have been fitted afterwards but is there any reason or benefit that someone may choose to leave this part off?

You only leave it off if you like the smell of gas fumes in the car. I would pick up a Haynes manual. It has pictures and tons of info on maintaining these cars.

What year is your car? The expansion tanks changed from metal to plastic in mid '74. This is the late '74 with the plastic expansion tank.

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I deleted mine,the fumes now vent into a fuel filter near the tank and then back into one of my air cleaners,I have very little fumes in the cabin,I plan to seal up the cap better as I only have the (cardboard) hard seal in it.
Pretty sure that 914 rubber have a better seal for the plastic cap?
Retained the plastic filler overflow and vent fitting and plan is to seal up the whole area where heater hose ,etc come through the dash bulkhead.
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It looks like on my car that a hose goes from the fuel cap area to the expansion tank then from there to a canister. Couldn't you just run the hose from the fuel cap area to the canister and by pass the X tank? Just a thought, I plan on keeping mine on.

I don't see why not if you are running carbs,not so with stock efi as the return fuel into the tank causes most of the fuming,I have no idea what percentage gets returned from what is delivered buy the stock pump.
Just my 2 cents and others wiser than me may comment,but all efi cars I have worked have some form of expansion tank,don't see a need with carbs.