KISS is an acronym for "Keep it simple, Stupid" as a design principle noted by the U.S. Navy in 1960. The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design and unnecessary complexity should be avoided. - Source Wikipedia
I think keeping things simple is one of the best bits of advice one can get whether it's in your photography, or any other area of your life.
Indeed, keeping things simple is a principle that has over time, been adopted by many disciplines from engineering to the arts to recreational activities. Here is another example of the KISS system taken from Wikipedia:
In film animation, "Master animator Richard Williams explains the KISS principle in his book The Animator's Survival Kit, and Disney's Nine Old Men write about it in Disney Animation: The Illusion of Life, a considerable work of the genre. The problem faced is that inexperienced animators may "over-animate" in their works, that is, a character may move too much and do too much. Williams urges animators to "KISS". - source Wikipedia
I also know that in scuba diving, the KISS principle is employed with rebreathers. The belief is that by making the rebreather fully manual, it's more likely that the operator will have a complete idea of what is happening at all times. This I understand, was due to many deaths from divers using automatic rebreathers that fail. It's a simple idea: make the user fully in control and that way there's less chance for things to go unnoticed.
I have a few KISS principles regarding my own photography. I don't suppose I'm the only one who does and each of us will have different approaches to our own working methods.
With regards to my digital-darkroom working methods, I prefer to keep things as simple as I can. I don't use multiple applications - I just use one and even with the application I use, I've learned to use around 5% of it. My belief is that by focussing on a restricted tool set, I have had the opportunity to become fully fluent with it, so much so, that it has become second nature to me, and my understanding of it has deepened over the years.
If I feel there is something I can't do with my current toolset, then I may enquire elsewhere. But so far after 16 years, I've not felt the need to. In other words, I only employ new tools or techniques when the situation requires it. Rather than being let loose in a candy store, I prefer to work with what I know.
The same for my choice of lenses. For the first decade I only really used two lenses: a wide angle and a standard lens. Both were fixed focal length lenses. Because they were fixed, I got used to how they rendered scenes and what their technical limitations were (close focussing distance, depth of field range), because they only did one thing. By using only these two lenses, I was able to pay more attention to practicing my visualisation. It was only after so many years that I started to branch out to other lenses.
I also have a process for my kit. I keep everything in the same place, so I rely on muscle memory. Put something back in the wrong place and spend time hunting for it later on. I've also preferred to use the same tripod head for years because I know it well, rather than be tempted to buy new ones all the time. I'm tempted just as much as anyone else and when I have strayed, I've gotten lost or confused for a period of time while I've settled into using unfamiliar kit. These days I try to adopt new equipment carefully and spend a lot of time getting acquainted with it.
Economy has a lot to offer us as creative individuals. By reducing down to what you most frequently use and discarding the rest, your workflow becomes so easy that there is less of a chance of it hindering you while you are in creative flow. Whereas conversely, if you aren't too careful and keep employing new techniques when you don't need to - your creativity may get bogged down in technical troubles.
The skill is knowing when to look for new techniques and when to leave them well alone. If you feel you're getting on well with what you have, then I would urge you to keep it the way it is. If however you feel you've reached the end of where you can go with the tools you have, then it's time to engage in new tools. Just don't do it when you don't need to, as that is the best way to overcomplicate things when they didn't need any fixing in the first place.
KISS - Keep It Simple ( Stupid :-)