UV lightmap size

Hello, I wanted to confirm with somebody from the official developers team if the information I keep stumbling upon on random forums is correct.
To perfect your lightmaps in UE4 for archviz people are suggesting to use ‘desired resolution minus 2 pixels’ size for your UV lightmaps instead of usual 64x64 or 512x512 and so on - is this correct?
To clarify: before importing the mesh into UE4, I unwrap the UVs, set my grid size to 1/62 (or 1/126 or 1/510 or 1/1022 and so on) in UV editor and follow the well known procedure of aligning the islands to grid and leaving 2-4 pixels of space between.

Thank you,

that is sort of true, but I wouldn’t use a grid of 62/126/510, but just leave at least one pixel on each side of the 0-1 uv space.
so if you have a light-map of 64, you basically only have 62x62 pixels you can use, minus the 2 pixel gap between uv-islands.
Keep in mind that if you later on decide that the lightmap needs to be 32 or 128, you need to redo the lightmap again.

So… if you have a decent lightmap, you can actually just let ue4 look at that lightmap, set the right lightmap resolution, and let ue4 recreate the lightmap in the same slot.
(auto generate lightmap) it will create the lightmap with regards to the pixels on the edge, and gap between islands.
BUT! it needs a proper lightmap to begin with.