There are numerous differences between spinning reels and baitcasting reels.  Both have their advantages and disadvantages.  Making a choice between the two usually depends on the user, what one is trying to catch, what the situations and conditions are.

Spinning reels are usually used by those who are fishing for the first time, and is ideal to catch small fish.  They have no settings for spool spin and lure weight which makes them easier to learn on using.  For spinning reels, the reel's guides are located on the bottom side of the rod which makes them easier to hold unlike baitcasting reels .  They can be placed on a flat surface or set on the floor because they sit upside down and don't roll over unlike the baitcasting reels that always does.  They work quite well with a 2 to 12lb line for BWCA (Boundary Waters Canoe Area).  Although they work quite well for beginners, there are some disadvantages on spinning reels.  If one doesn't know how to cast properly with finesse, the line of the spinning reel tumbles off the end of the spool.  Also, when catching the big one, spinning reels often cause nasty twists on the line which makes it better to use baitcasting reels when catching big fishes.

Baitcasting reels are often used by those who have experience on fishing.  It requires the fishermen to have knowledge on the weight of the lure, the distance of the cast and the friction of the spool.  Baitcasting reels are ideal for big fishes with their trolling -only rods.  Another advantage is that the drag doesn't make a lot of noise, or no noise at all which is a negative point for spinning reels, and on the contrary the fishermen have to use their thumb on the spool to know if their line is going or not.  Unlike spinning reels, the line of the baitcasting reel dies not twist when cranking the reel around and around, since the line goes in and out in a linear direction and comes back the same way.

Using a spinning reel or a baitcasting reel when fishing may have their pros and cons, but it all boils down to what happens when there is a catch:  making sure that the rod tip is up in the air and keeping the line tight constantly, so that the fish doesn't go out of the water.