Hello! I've being a long time tweaking this and that in my CC and I think I sort of get what certain flags do but others I don't. I mean the ones visible in the Footprints menu from TSRW, for example. If someone knows well what is their function, could you please enlighten me so I can use them properly? I am curious about:

FootprintPolyFlags

ForPlacement = ?
ForPathing = ?
IsEnabled = ?
Discouraged = ?

IntersectionFlags

Sims = ?

SurfaceTypeFlags

Air = ?

The Footprint/FTPT usually concerns how an object snaps/slots and how Sims 'view' it in terms of being able to walk through it or not.
You might be able to get a better idea looking at it with Footsie, which is one of the plugins for S3PE from here I believe.
Opening a few EA objects and opening their FTPT might help you get a better idea of what does what.

Intersection flags are about what the object can clip into/snap flush against, the Sim one specifically allows an object to be walked through.
Surface flags are about where the object is meant to be placed.

The first set are called 'Area' flags in Footsie and are a little more ambiguous for me to speak on from memory, I'd recommend checking what different kinds of objects have them.

Thank you very much for your reply. I did have a concept of footprint as such, but still some flags seem confusing to me. For example the "Sims" one I tend to find activated in a lot of CC which confuses me because I don't think you want to allow a Sim to walk through a dresser for example, but I encountered that a lot. Also the one called "Air" is activated in wall lamps or clocks but not in the telephone, don't they all of those objects stick to a wall? Why some do need "Air" and others don't?

A combination of object flags in the OBJD + the FTPT + the appropriate script come together to make the magic happen, so some don't mean much without the other.

From looking at an EA dresser, it actually has two FTPT and there are references to them inside the script. An educated guess, the one that allows Sim intersection is probably related to the animation of using the object so Sims are allowed to route closer than they are usually allowed. Sim intersection is not enabled on the main placement footprint.
'Wall' flags seem to be related to shiftable items, so wall phones (and mirrors) don't have these enabled because they have animations linked to the exact height they're at. The wall-snap is controlled in the OBJD instead, at WallPlacementFlags.
'Air' is definitely more ambiguous. Maybe even related to where Sims swivel their heads when they look at an object as they pass by.

Some CC could be reusing these EA footprints, so they might not always be present in the package- or if you're using TSRW, it may only be showing you the first one it decides to load. There can also be unused settings left over from whatever creators cloned from.
I'd recommend using S3OC + S3PE to look at EA items when experimenting with things, just to rule out that you aren't misled by those kinds of variables
Figuring out method in the madness without knowing what all of this looked like through the tools EA had is quite a task

Thank you for your reply and for your guidance. :D