Since PE2/3 more popular these days, better to make an explanation following differences.
RunFrom RAM - CD are creation of Nightman on pe2.
Since Nightman made such successfull organisation, it is used by all following pe2/3 projects, with exact same organisation.
RunFrom Ram= Means having application on a writable environment. (additional writable space available via RAM)
With PE2/3, this VERY MOSTLY means having application inside image-wim.
There is significant organisational difference
between Gena and pe2/3 organisation default behaviour.
With Pe2/3, some selective targetdir folders
packed to image-wim, and others left to be on cd.
With Gena (+bootdi/wimboot) ALL targetdir folders
packed to image-wim/img
Hence, on Gena, when image boot (bootdi/wimboot) used, 'RunFrom Ram' is not required like pe2/3 since all files inside image ;).
With Gena, 'RunFrom Ram' become more useful when CreateISO used with no fbwf.
'RunFrom CD' become more useful for Gena image boot (bootdi/wimboot) to get image size smaller.
following significant organisational difference
here is a good example to keep in mind:
When you create a folder at targetdir, and put files in it (ex: \ppapps\)
Pe2/3 -> \ppapps\ folder will be on cd - NOT inside image-wim
Gena (wimboot/bootimg) -> \ppapps\ folder will be inside image - NOT on cd
Since getting smaller image is more valuable for ALL projects,
On Gena, either \ppapps\ folder can be added to exclusion list, or more practically one can use "Put Files for 'RootCD' Here" button to copy files to cd.
ps: On Gena wimboot/bootimg both have same behaviour so testing with one of them would be enough to see the difference between create iso.
Well, these are basic organisations but it requires some practice to understand fully,
Since PE2/3 users verrry mostly (naturally) use image-wim boot, it is easy to figure out there,
On Gena, it is still easy ;) but requires some practice to understand fully since there are many optional settings to test with.....
I hope above useful.