Small flies certainly have their place.
Whether imitating insects or other types of small forage, a downsized fly is often a great choice to "match the hatch" when it comes to accurately representing these little morsels. With that said, of course all fish don't always hunt for tiny food 100% of the time. Even fish like rainbow trout will munch on a pretty substantial meal from time to time. A prime example here are bass; in particular largemouth bass. With a mean attitude and a huge mouth, they will often hunt down prey that’s shockingly large!
In conventional bass fishing, there's the standard set of baits like jigs, plastic worms, spinner baits, and crankbaits.....to name a scant few. Since roughly around the early 2000's, though, the swimbait market has literally exploded. Sure, they come in all shapes and sizes, but big swimbaits have gained massive popularity and garnered almost a cult-like following with some folks. The reasons for this are simple—the "big baits" are certainly fun to fish, but they also crush huge bass when nothing else will.
I'm surprised there isn't more spillover of the swimbait angler mindset into bass fly fishing.
What I mean here is, I don't really hear or see much about a legion of fly anglers going out there and consistently chucking truly big patterns for bass. Pike and musky hunters do it all the time, but why not for bass? I understand casting these big flies can become a real chore, but there's ways to manage that.
If you're interested in giving big flies a try, you'll need some stout tackle (a 12 weight might be useful...not joking!) and you may have to tie your own custom patterns. When tying, using synthetics that absorb little to no water is a great way to keep big flies more castable. If tying isn't your thing, another option is to check out what's available to saltwater anglers. Certain flies crafted for fish like trevally, sailfish, and dolphin should work for big bass!
Here are some key reasons you may want to upgrade the size of your bass flies....
Get Their Attention: The bigger the fly, the more attention it gets....period! A larger fly has more presence and displaces/moves a lot more water, thus making it easier for fish to both see and feel from a greater distance. In situations where the water is of average to clear clarity, this gives you the option of spacing your casts out much further apart when trying to locate fish over a vast area.
Make em' Move: Adding to the point above, a big fly with more presence can coax a fish to move further to intercept it. If there's an eight pound bass laid up along a grass line, do you think it's more likely to swim ten feet to eat a two inch woolly bugger, or a six inch streamer imitating a rainbow trout?
On the flip side, a big fish might not want to move much at all. Many anglers have a preconceived notion that bass are always aggressive and will strike at just about any decent-looking fly, but that's not the case. If a big bass is lazy, putting a big fly in their vicinity may result in a strike. Depending on conditions that fish may not want to move more than a few feet, but the bigger the meal often the more interested she’ll be.
Big Bites: As the title implies, big flies can catch big fish because these flies represent large, calorie-dense meals. A big bass won't eat too often, but when it does it has to really count. I always find it interesting how I can fish through an area with a more "standard-sized" fly and pick off some average fish, but when I come back through with a much larger offering all of a sudden I get that bigger bite. I've fished areas where I swore a five pound bass didn't exist, but by switching to something much bigger that fish finally revealed itself. Additionally, while a big fly will generally get less bites overall, don't think that the average bass will totally ignore them. It's really surprising what a smaller bass will attack!