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 them, so much so, that they have come second nature to me.
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.
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 :-)