A process is a set of steps that produce a more or less predictable result.
If I shoot black and white film, develop it according to directions, and then take some more steps with some more materials, what results is black and white prints.
If my process involves placing a flower in front of the camera, my process is one which produces pictures of flowers.
There are tons of photographers with processes that relate to subject or rendering, often both. Most so-called street photographers have a process that involves setting their camera to black-and-white, and then taking pictures of people outside in an urban environment. This produces, surprise, black-and-white pictures of people in an urban environment. To many photographers, that's what street photography is.
Other photographers have processes that are about light, or lighting. These people will urge you to Master The Light or something similarly fatuous. Among these guys, consider the 500px-popular landscape photographer. These landscape guys might have a process that involves waiting for certain times of day, certain weather conditions, and so on, and then taking wide angle pictures of land. Or water. Or whatever. Then they might apply a process of photoshop activities. The final result is usually more or less the same as everyone else's landscapes. It's brightly colored, it's pretty, the moving water is rendered as a freakish mist, and the whole thing would look terrible on a giant canvas wrap print above the couch.
The trouble with all these processes is that they are all about subject and rendering.
If you want to produce pictures that look a certain way, if your goal is to make pictures that look like Peter Lik's, or Eric Kim's, then your process should be about subject and rendering, because that's all these guys have going on. You follow their process, you get their results. You add a little of your special sauce, you get their results with special sauce. It's pretty straightforward. It's not my thing, but if it is your thing, you shouldn't be ashamed. Well, no. You should be ashamed of yourself, but only a little bit. It's ok, we all have faults.
If you want to produce pictures that have a certain idea, a certain feeling, a certain emotion, and you want them to make more than one picture that connects to the same idea, feeling, or emotion, then a process is a good idea here as well. It's just not a process that's entirely about subject and rendering, it's about idea and use as well, where I use all these words in the sense defined in the linked essay.
Another way to put this is that if you have a clear idea in mind then your pictures have a chance of being connected at that level, of all expressing the common idea, or facets and variations on that common idea. It is likely that subject and rendering will tend to follow along as well, since idea is really expressed through these, but it it by no means certain. A portfolio which uses a handful of radically different subjects and renderings to express similar ideas is going to be pretty interesting, and certainly won't suffer from the problem of just being the same damned picture over and over.
As always, the usual caveats about the blurriness of lines between subject, rendering, and idea apply here.