While I understand the mechanical differences between the two, I'm still lost at understanding what conditions/lure types/overall conditions dictate which reel is better.  Can anyone shed some light on this for me?

Most tend to think of spinning reels for throwing light weight baits that a casting reel won't do well on. I'm here to tell you though, get a good baitcaster, match it to the right rod, and then casting light weight baits becomes a reality. But to achieve that same level of casting distance with a baitcaster will probably require a lot more money than a spinning reel with the same ability. A spinning reel's cast is purely dictated by the rod action (how well it loads up under the lure's weight), free flow of the line through the guides (meaning how well the guides eliminate friction with proper spacing and guide material used in construction) and the type and size of line you use.

A casting reel's cast distance is influenced by all those same factors but also the spool turning during the cast comes into play so having good, no...GREAT spool shaft bearings come into play there as well. But getting GREAT bearings in a reel requires you spending some decent money. You can use any old cheap spinning reel though, a $20 reel will cast as well as a $100 reel. Now......how well they handle the retrieve, drag paying out during a fight, how long they will last.......that's a different story and that's why you want to give a bit more for a spinning reel as well.

I think some people though, in order to get a baitcaster and save money they go cheap and that limits how well it casts light baits cause cheap reels contain cheap components, so they still need spinning reels too for throwing light stuff. I'm not 100% sure you can get by without a spinning reel at all but since I started using better equipment in terms of rods and casting reels, I've noticed I need my spinning rod less and less. I go whole trips now and never touch them sometimes.  And then there's some people who simply are not able to use a baitcaster so they HAVE to fish with a spinning reel.

Otherwise I use a baitcaster for control of the lure, especially heavier lures, I can cast the bait more accurately with a casting rod due to the way I throw it, and I can use my thumb to feather the cast down so that the bait lands in the water quietly instead of the big SPLOOSH that the lure makes when throwing with a spinning rod. Only use I still have for a spinning rod is for lures that I simply cannot cast with a baitcaster, such as a plain ol' 7" Zoom worm on a 3/0 EWG hook and no weight. My baitcast reels cast this, but not over 40 feet so until I upgrade that far then I still need my spinning rods.

Of course some others will also say that there are maybe some techniques that simply work better with spinning rods/reels, and I'll let them tell you about those cause I don't know specifically what those might be. This is my take on it though.

Excellent post!

I fish bait casters exclusively.

To fish the lighter lines I use quality gear. Drop Shotting is done with a Curado E7 with 8# test. I fish this on an Allstar 7' Medium, fast tip, Speckled Trout Rod. It has enough backbone and is forgiving enough that I don't break off when setting the hook.

I'll be the first to admit it's not for everyone, but it works for me.

WOW!  Very informative Rooster.  Long casts and tight lines Sir.