The greatest difference between spinning and casting gear is the way the line is managed. Spinning gear uses a rotor to pull the line off the rod, turns it 90 degrees and wraps it around a stationary spool. Casting gear takes the line off the rod and places it on a rotating spool via an oscillating line guide.
Spinning gear excels with lighter baits, lighter lines, and finesse presentations. The nature of how the reel manages line makes heavier/thicker/stiffer lines difficult to use on spinning gear as the line will unspool and cause loops and tangles. Casting gear excels with heavier lines, lures and power presentations. Thinner lines will dig into itself on the spool and if you do not have proper balance with your set up, it can result in a bird’s nest, also called a backlash.
The way you hold the rod and reel will also play a factor in how you use it. Spinning reels sit beneath the rod and allows you to wrap your hand around the foot of the reel facing down. A casting reel is typically held in the palm of the hand, with the reel on top of the rod, this is often referred to as palming the reel. This affects the balance of your rod & reel combo and how you apply pressure against the lure and fish.
Balance is the key when holding a rod and reel and should be considered when deciding what type of set up you will want to use for the desired presentation. Not just the balance of the rod and reel in your hand, but balance between rod, reel, line, lure/weight.