Retouch is not always mandatory and requested by a client. All depends which type of service is ordered.
Retouch can be devided into different categories:
1. Editorial images and simple reportages.
In this case changes to content are not allowed, and photographer can play in post processing only with lightning, contrast, sharpness within the limit: the content should be understood in the same way like on not retouched photos. No objects added or removed.
2. Reportage with custom retouching.
This type is applied to reportages which suppose to be delivered enough quickly, with maximum presevation of original content. It is not Editorial type of reportage. Examples: basic packages for engagements, weddings, anniversaries, any kind of other private events, basic packages for portraits.
What is possible to do within this price and time frame? Of course, light, contrast, sharpness. And something what can be done on client's demand: light retouching of images content. Examples: make a person more slim(of course this should be recognized as the same person), remove birth marks, scars and sicatrices, whitening of teeth, spots on clothes, rubbish on the pavement, cigarettes.
3. Deep editing. This can include all above plus cut-out, more deep face editing, more slimming, removal of clothes defects, applying of different filters, vignettes, frames, effects. Seems no limit, but needs more time and is more costly. Usually such type of editing is applicable for glamour portraits, top weddings packages, official presentations portraits in high resolution.
The client usually knows what he wants, but sometimes the wish is unrealistic. The photographer helps to find a correct balance between "i want" and "it is possible" within a client's budget.
This collection will be extended and more examples are on the way.
Example of skin editing