"Clean processing" is a term you'll see frequently on photographic forums, and especially in my Facebook group. To a degree, everyone has their own interpretation of the concept, but maybe it's new to you.
In a nutshell, a clean-processed image is one to which it's not obvious that any editing has been performed (even if it has). The kind of image that makes somebody say "Wow, you're a good photographer!", rather than "Gee, you're good at Photoshop!".
A clean-processed photo has no particular effect or style applied, and as such, it should sit as comfortably in your portfolio in five or ten years' time as it does today. However, it does provide the basis of all other editing styles. Consistent clean processing means consistent and predictable results from your artistic editing, especially if you use actions or presets.
Of course, even within the narrow description of "clean", there is room for personal interpretation. You may prefer your images warmer or cooler, or brighter or darker, or richer or paler, than the next person. But in general terms, a "clean" image is one where the whites are white, the blacks are black, and the grays are gray.
Is it quick?
Maybe, maybe not. It depends on how good the original photo was. Clean processing might take a few seconds, or a whole hour. The point is, nobody can tell.
In a way, clean processing is like housework. When your mother-in-law comes to visit, and finds your house tidy and spotless, she doesn't know if you've done a five minute spruce-up, or hours and hours of hard labour, to get it looking that way. (In my case, invariably the latter!) She just sees a clean house.
If you take a look at my portfolio, you'll see examples of clean processing that took an uncommonly long time, due to difficult lighting, or equipment malfunction, or whatever problems can arise from time to time. But for most photographers, most of the time, clean processing should be quite fast.
Is it easy?
Again, it can be. It should be. And it usually is. Those times when your lighting and your camera settings were perfect, the processing is a piece of cake, once you know how.
But when the photo wasn't perfect, clean processing gets hard. Not just hard - the hardest. There is no greater challenge in post-processing than making a ballsed-up photo look (a) not ballsed-up, and (b) not edited at all.
These are the skills that I have devoted my career to perfecting. So far so good, but still a way to go.
Postscript
There's one more thing I need to mention ...
Clean processing is the only type of editing that can be constructively critiqued. It's the only time you can legitimately say "Your such-and-such is incorrect" or "It needs less such-and-such", etc. In short, it's the only type of processing to which rules apply.
The moment you apply any kind of artistic effect to your photo, the only "critique" that can be offered is an expression of personal opinion - "I like it" or "I don't like it". People can still legitimately offer feedback about the photographic aspects of the image (composition etc), but not the editing.
This is why I have no patience for people posting artistic editing for CC in the AD group. There's no point to it. Your hazy crap (or whatever the fad of the week is) will get no gushing praise from me. I operate on a "guilty until proven innocent" basis - unless you show me a clean-processed version of your photo, I will assume that you've added the effect to disguise your shortcomings as a photographer, or editor, or both.
I want you to prove me wrong.