The weight is worth having if for no other reason it holds the record in place while you clean it with your dust brush. I have gone back to the inner and outer clamps similar to what I had on my Merrill Heirloom table. They flatten out minor imperfections and add 3 pounds or so to the rotating mass - both good things.
There are a bunch of swings and roundabouts to this one...
Increasing weight will alter the resonant frequency of the TT stand (all of it, from the ground through to the platter, regardless of whether the TT is a suspended design or not!)...
Whether this is for the better or worse, will depend on the stand, the turntable suspension and even the floor it is on (whether it is a concrete slab, or traditional floorboards...)
There is no simple answer as to whether it will improve things or not - in different cases it will go in different directions!
Then there is the additional weight on the platter bearings - this is almost always a negative - some TT's are sufficiently heavily engineered (over-engineered?) - to shrug off the additional weight, others aren't...
One alternative (which I use) is to use a lightweight clamp rather than a massive weight - the end result can be well nigh identical without affecting resonant frequency or platter bearings.
Finally - yes something that pushes the record down onto the platter surface/mat is especially useful for records that have slight warps and this flattens them - it can also affect the damping of the turntable mat itself (which may be a positive or a negative, and will vary depending on too many variables to review).
I am NOT saying don't use a weight or clamp - But if you are going to add substantial mass to your TT system, you should consider what it might do to the various resonances and springing/damping of your entire TT system.
People really should have a go at measuring the resonances that get transmitted and/or damped through their entire TT system... best way is to stop the TT motor, and (GENTLY) lower the needle on the platter surface... then measure what comes through when you stomp around the room, or play some music loudly.... it will quickly show up the resonances that come through vs the ones that get damped... adding mass or adjusting (firming or softening) the springing of the entire system, or adding various sorts of absorbing/damping mechanisms, will alter these... and you can measure them.
One of my TT's was well nigh unuseable on my old style floorboards... (the suspended ones were fine, the solid platform ones did very badly indeed!) - until I added mass (60cm x 60cm concrete pad... serious mass!), sorbothane layers (damping and springing - both under the concrete pad, and under the feet of the rack) to the platform (rack) - after which the two types of TT's ended up much of a muchness... It wasn't expensive in the end, and along the way I did experiment with some of the more expensive options (mag-lev)
