I don't think anybody will disagree that wading is important and often mandatory for catching fish.
However, I've seen wading have the opposite effect. The disturbances caused by being in the water or merely just your presence standing there can impact an area and shut the fish off or totally scare them all away—even if you're being ultra careful. Current and chop can definitely help mask your presence when wading, but when the fish and conditions are touchier, staying out of the water might be the very best way to go.
Of course, not wading can also mean not being able to reach the juiciest water or it can severely hamper your ability to make the most effective presentation. Nobody wants that! Wade if that's the way to go, but sometimes you don't really have to or shouldn't at all, and doing so can put you at a disadvantage. Big time.
I only wade if I absolutely have to or if I know it won't hurt my success. Here's three points to keep in mind before taking that first step into the water:
Keep Quiet- When you wade, you can make excess noise in the water, silt and junk gets kicked up, and there's a "push" of unnatural waves/ripples when you move around. Being someone who has sight-fished a lot in shallow water for many years, I've witnessed fish zip off to parts unknown from simply wading—even relatively slowly and carefully. To keep the stealthiness at level 10, I say the very best practice is to stay out of the water if at all possible.
Observe First- When fishing an unfamiliar situation, it can pay to just stand on the bank and observe for a few minutes. Are fish cruising in close? Is there some good holding water right near the bank, like a little pocket a few feet out or maybe an undercut bank just down the shore? Before you go sloshing out there, make sure you won't be trampling through or near an area that might initially produce a bonus bite or two. The best water may very well be further out, but there might also be some good stuff in close, too!
Cast it Out- Want to wade out to make casting a little easier? Why not just cast further? If you can reach the spot you want the fly to go and your overall presentation won't suffer, consider just making a longer cast from the bank. This can be really important if the water is very calm and/or shallow. A longer presentation is always more sneaky anyhow, so if the fish are really touchy you're always better off putting more distance between you and them. Staying on shore also gives you a higher vantage point to more easily see fish, key holding spots, etc.
So the next time you're ready to start wading out, take your time and think before first dipping your foot in the water. Look around, size up what's going on immediately nearby, and determine if wading is the very best approach to take right away!