The gear ratio of a reel basically means how many turns the rotor will have against the handle. A gear ratio 6:1:1 means the rotor will turn 6 times per turn of the handle.
If you are fishing lures that need to be fished faster, then a higher gear ratio is your choice. For example, fast twitching jerk baits, blades, or even topwater baits that need a faster more accurate control speed, this gear ratio is excellent.
A low gear ratio can be effectively used on lures that you want to present slower. Predator fishing for muskie, pike etc. with glide baits, tail baits or bigger swimbaits with a slow presentation. Then you should go for the lower gear ratio.