I cast right handed, so that factor doen't change. I have been casting bait casting reels since the mid 50's when these reels were only made with handles on the right side to take advantage of the handle being positioned at 12 o'clock to aid in casting distance with the spool shaft riding on the bearing on the opposite end...the old knuckle busters! Reels have gone though a lot of design changes with multiple bearing, however still cast better with the handle upright.
The biggest downside for me is in the way I hold my rod, hand mostly in front of the reel, so I can run the line between my thumb and index finger. 60+ years of training my left hand and finger to send feed back to my old brain can't be undone in a few years and why change when it works for me! I can keep up with anyone that I have ever fished and catch my share of big bass.
If you are a jig angler or other soft plastics that require instant feed back that a bass has the lure in ti's mouth, you will never realize that fact faster relying on your sensitive fingers, instead of the rod. If you change to the left hand reel; try to learn to feel the line as it comes off the reel, this will improve your strike to hook set ratio, right or left handed..
Tom