Lighting with default lights or Meshes (Emission) + Volume Scatter. Pro and Cons?

Hello everybody,
I saw many tuts about lighting where people use meshes (planes) with Emission shader to light the scene, sometimes using also a Volume Scatter node as well.
I would like to know what is the difference between this technique and using instead of the normal default lights.
And what is the Volume Scatter for? Is it useful in both techniques?

Thanks in advance for an answer!

I use emission geometry as little as possible, maybe go as far as cheat it with regular lights if I can. And when I do, i.e. to emission texture a computer monitor or something, I may turn off MIS so that it doesn’t compete with the actual scene lighting.

So far in real projects, I have not had to use emission geometry to actually light a scene. It’s usually daylight (with or without direct sunlight) and/or interior office lighting. Emission geometry is only for camera rays.

I don’t know about volume scatter. I don’t have to deal with volumetrics thankfully.

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Yes, okay,
maybe lighting with Emission meshes is great for “all CGI project”, so not Image Based Lighting, i.e. product visualization.
Thanks for a reply!

Well, they’re great for everything if you can afford the longer wait. Better than lamps even, as you don’t have to do any double work just to get them visible to camera (lamps can’t be made camera visible yet).

Doesn’t matter what you render. I used 11 lamps of various everything to do a product visualization of a simple sheet metal box. Yeah you can get a decently looking render using IBL at no setup cost at all, but you have absolutely no control over getting the right edges highlighted, part separation, background separation and so on. I had a dark object featuring some metal part (front and back have different details), on a dark background - I got nowhere I wanted to go using IBLs so I reverted to manual lighting.

So, Emission mesh take longer time to be render (in EEVEE e Cycles), right?