on a casting rod it effectively moves the line to the bottom of the rod. There are a few different methods to do this but most involve using the 1st 2-4 guides to roll around the blank until they are all on the bottom.

a few benefits -
- solves line scrub when using smaller running guides.
- eliminates twisting/torque when fighting fish

most will also say that it lest you use more smaller guides which saves on weight and cost - however that really goes back to line scrub because that is the really the only issues with using all smaller guides on a conventional wrap.

that said - there really are no disadvantages to it - i build about 90% of my personal baitcasting rods as spiral - with the exception of top-water rods. The biggest hurdle for most to overcome is their perceptions of how it will work based purely on how it looks.

here's a simple spiral using full sized alconites (8df, 7df, 7sf, 6sf runners)