There is nothing worse than a big ugly len flare generated with photoshop.. we can all agree on that.
But lens flares can really make a big difference to an image if used in a subtle and realistic way. Sun glare from specular highlights are a very common sight in photos and of couse as observed with the naked eye. If you look at a car on a sunny day you can see what I mean. Shading a lighting in 3D can not really replicate this well. The same can be said of glow and flare from lights. Shader glow is also pretty poor for replicating this.

In the following examples show the basic technique I use to replicate lens flares, secular highlights, and light glow.As I do illustration they really apply only to stills.

For the light glow and flares I have taken a fast exposure of some real car lights and screened them on to the image. For the specular sun flares I took a fast exposure of the sun reflected in a car bonnet (or hood if you prefer) which was painted metallic black. This was screened over the image where the CG specular highlight appears.

I have taken a whole library of flares from various light sources and reflective surfaces to capture just the highlight. I use them a lot in arch viz where there are artificial light sources. But also the augment any exterior image.An added benefit of this approach is the inclusion of micro details on the surface. most painted and polished surfaces have these micro scratches on them that get picked up around the highlight and thus in the photo... they add a nice touch to the rendered image.
Here is an example of this with the original photos of the flares.

That's All

Thanks for taking the time to read this article and I hope it was enjoyable.