I'm using CS6 in Mountain Lion (so don't know if this affects other versions / platforms OS's) and have noticed something odd saving a file.
I have a document that is 2048 x 1536 with two layers in it, one is a bitmap, the other a vector shape with 7 points (a circle with a play sumbol in it).
Saving it creates a PSD of 18.3mb.
Deleting the shape layer and saving it gives me a file of 9.2mb.
So by my maths, that's 9.1 for a vector shape with 7 points.
How is that even possible?
Delete the bitmap layer and save with just the vector shape and the file is 249k.
What's going on?
If you have set the Maximize Compatibility setting in preferences, not only is the shape layer saved as metadata, but there is a flattened composite image created and saved with the PSD as well. It could be that it's not able to compress that flattened composite particularly well.
If you don't have other applications or older versions of Photoshop needing to read the PSD files in your work environment, you may experience a significant savings if you set Maximize Compatibility to Ask or Never and save without maximum compatibility.
Just to be clear, older versions of Photoshop WILL read files saved without maximum compatibility if they don't contain features only available in the later (saving) version of Photoshop. When the "compatibility" process is invoked, the older version (or external app) will revert to reading the flattened composite, which isn't always useful anyway.
Thanks for the quick reply - that's exactly what it was. File now saves at 10mb.