Reels let you control your fishing line, how it's paid out and how it's retrieved. In addition, reels have a "drag" system that is used to pressure the fish during the fight. Finally, reels provide mechanical advantage to enable you to reel in that whopper.
Spinning reels are popular with many anglers because they are versatile and easy to use. The key difference from conventional reels is that the spool is mounted parallel to the rod on the underside of the rod and that it remains stationary when casting. During the cast, line is uncoiled from the fixed spool by the lure or bait as it flies through the air. When retrieving the line, an arched rotating pick-up mechanism or bail lays down the line on the spool, simultaneously reversing the twists that resulted from casting. Spinning reels are an excellent choice for light tackle and easy to use by less experienced anglers.
Conventional reels have spools revolving on an axis perpendicular to the rod. There are a tremendous variety of conventional reels, ranging from compact baitcasting models to gargantuan multi-speed offshore saltwater reels. In general, conventional reels require a bit more technique when casting because the inertia of their whirling spools can lead to backlash and tangled line.
Power Assist electric reels are used for deep dropping to depths of several hundred feet or for kite fishing. They're big, fast conventional reels with an electric power assist. Generally they clip onto a 12V battery, plug into a receptacle on deck, or use their own Lithium battery pack. They include an expanding range of control panel features like automatic jigging functions, and LCD readout depth counters.
A rod and reel work together to form a system. Therefore, the most important consideration in choosing a reel is to match it to the rod you'll be using; light reels for light action rods, heavier reels for beefier rods. That said, you still have many options to consider when choosing a reel.
Spinning reels are the easiest style for most anglers to cast with. However, they don't have the sheer cranking power of conventional reels, so they aren't (usually) suitable for large saltwater fish. Conventional reels require a bit more skill to use because of their tendency to backlash on casts if the spool isn't properly controlled by the angler's "educated thumb" or, on some models, a mechanical backlash prevention mechanism.
What do you get when you pay more for a reel? Whatever reel configuration you choose, more expensive reels provide either smoother action or improved ruggedness–or both. Experienced anglers will tell you that a reel that operates smoothly while casting, retrieving and fighting a fish is well worth the extra cost. They're not only more comfortable to use for a long day on the water, but they significantly reduce the likelihood of losing a fish due to problems with a jerky drag or balky retrieve that can snap your line. If you'll be fishing in a corrosive saltwater environment, choosing a reel made from non-corrosive materials such as graphite, stainless steel and anodized aluminum is a sound investment for both the added durability and your fishing enjoyment.