Film Simulation is a post production process applied to a digital image that aims to simulate the appearance of a specific make of film, e.g. "Kodak Portra". A useful purpose of this technique is to allow Hybrid Photographers to achieve a look, from the images captured with their digital cameras, that appears similar to the results they are getting from their still film cameras, thus enabling them to achieve a level of appearance consistency between both platforms.
As an exclusively digital photographer I also use film simulation quite a lot, because I like the "nostalgic look from film" appearance that the process gives to my Street Photography shots. The simulation presets are used within my Adobe Lightroom workflow, and can often impart a timeless look to the resultant photographs.
I have experimented with presets produced by two companies - “VSCO" and "RNI ALL FILMS". Both have great reasonably priced presets. However, recently, I have been considering trying out the Ilford Pack from "Mastin Labs" and hopefully in the next few weeks will get a chance to evaluate these presets too. I hope my results will be as good as the reviews suggest. Watch this space.
Of course, film simulation all comes down to one's personal preference. Some photographers prefer the look of digital imagery over that of film as it generally exhibits very little "noise", while there are others who like to rack up the "noise" level - like the 3200 iso grainy look from Ilford Delta film.
I currently only use monochrome based film simulation - mainly Ilford’s "HP5" and "Pan F" - but in the future I may also consider using colour film presets, such as "Kodak Portra" or "Fujicolor 400" for some of my Street Challenges.
Now remember, these presets are not one click wonders. They can give results that are very close to a film, but I do recommend that you try adjusting the settings to achieve your own look.