Have you ever been out deep sea fishing aboard a party boat? A lot of folks that go out on these trips just want to get away for the day and aren't serious anglers with a ton of gear. As a result, many of them borrow a rod/reel setup provided by the crew, which may include a conventional reel that lacks a levelwind. Thanks in part to their simplicity, these reels are usually pretty rugged and can withstand the daily punishment of saltwater and novice anglers. That simplicity comes with an associated annoyance, however.
Back when I used to occasionally fish on these boats, I still distinctly remember the hard life some of these combos endured. Chipped blanks. Busted guides. Corrosion. And, of course, lines that weren't reeled onto the spools evenly. Since most folks tended to just crank without leveling the line with a finger, the line would get unevenly wound onto the reel's spool—sometimes outrageously so. Visualizing the most lopsided examples actually still makes me chuckle! Since fly reels lack a levelwind mechanism, care should be taken with these reels, too.
Whether I'm simply reeling-in an empty line or actually fighting a fish from the reel, I always take the extra step of manually leveling the line onto the spool.
When fighting a fish, I'll lightly hook the line under the index finger or pinky of my rod hand and sweep it back and forth as I crank to ensure even line distribution on the spool. If I'm reeling-in line with no fish attached, I'll trap the line between two fingers (typically my pinky and its neighbor) and use those fingers to guide the line as I reel. Trapping the line between these fingers provides the necessary tension to pack the line on the reel nice and firmly.
When the line lays evenly and tightly on the spool, it won't rub against the reel frame, dig into itself, or bind up. The line will flow off the spool more fluidly when you strip off line or, more importantly, when a fish pulls drag. Leveling the line not only helps it lay tightly and evenly, but doing so can also help knock off extra little tidbits of debris or filth from the line.
With all of that said, I'm always cautious while fighting a fish—especially a big and/or fast one.
Fingers can get burned by the line or cut by backing (like gel spun) as a fish peels off quickly. When a fish surges (especially into the backing), I'll often relax or straighten my finger to release the line completely and let the drag do its thing. I'll either put that finger back on the grip with the others, or I might keep it near the line as in the picture above. Sometimes, especially with smaller fish or in less-demanding situations, I'll even just leave my finger hooked onto the line very lightly which keeps line contact minimal yet still allows the fish to pull drag freely. By keeping a finger "at the ready" on or very near the line, I'm able to get back to reeling and leveling line slightly quicker since my finger is already in or almost in position. One final note here is that gloves can be a great insurance item both against sun damage and line cuts/burns—especially those with full or extended finger coverage.
Another time I try to level my line is when I hook a fish with a bunch of loose line still off the reel, but I want to get that fish on the reel quickly. At that point, I'll firmly pin the line between my index finger and the rod grip, then trap the loose line coming off the reel between my pinky and fourth finger. Doing this, I can crank the loose line onto the reel under a bit of tension from my fingers, and do so evenly by guiding the line with those two fingers.
Keep it neat!