I do it but not sure why?Anyone shed some light on it? :-[

Push the weight down against the eye of the hook  and watch how the hook turns in.  I would imagine this increases the success of hookups though I'm not sure what actually happens on the hookset.

Makes sense to me.Thank's NOVA

The main reason is to keep a heavy tungsten sinker for damaging the knot. For very thick surface vegetation, some fishermen use sinkers heavier than 1 oz.

I tie a snell with a uni-knot.

Was just watcing a video on another site about this topic. 

The Pro said that you should only use a snell when you are using braid because mono and floro will cut its self and it won't be a strong connection.  I know this is true for floro but I'm not certain that mono wouldn't work since they've been snelling hooks with mono for eons.  Still I plan on trying it this year when I'm out flipping.

There was an episode on Classic Patterns with Terry Scroggins flippin mats in Florida.  He demonstrated the snell knot and the result of lifting against the weight.  It did cause the hook to rock up.  His comment was there is generally a layer of silt that can cover a bait but the rocking will expose it and the rocking equated to a tremendous increase in hook ups, almost always in the bass' "nose." He's pretty good at what he does.

I've also heard that when you peg your weight never peg it tight against you lure instead leave a 1/2" or so between the two allowing line movement. The reasoning is a bass of Hawg proportions can clamp down on the weight hard enough not to allow movement required for hook set.

I've seen this especially with jigs 

On the protecting the knot thinking,why not use a plastic bead like some people use when worming to protect the knot?Do any of you guys do this when flipping?

The biggest reason for snelling is to increase your hook ups. If you let the weight free fall against the hook, watch the hook pop up. Now imagine that in the fishes mouth. I only snell my knot when punching. Your hook up ratio will go up, and the hook is almost always in the roof of their mouth hooked solid.