Coring is used to stabilize and/or adjust weight with no cosmetic impact. It runs the entire length of the part it runs through, thereby giving added stability to the entire length. Full splice also contributes to stability and weight distribution but does not extend as far as a cored part. It does have a cosmetic value. A full splice also eliminates the 'A' joint, which could be why they are considered to be stiffer. I have yet to build my own splice, so I haven't dealt with it yet or been able to test two otherwise identical cues with that one difference. There are plenty on here who know more from their own experience.