Nelson Studs vs. Puddle Welding

Maybe.

You should ask the engineer who did the design.

Why do you need to disassemble some sections later?

I would consider the puddle weld to be a stronger attachment so long as you are sure of your final Assembly.

They do, when you place concrete deck over the steel decking and the designer has intended the studs to act as shear connectors so the concrete and steel act together in a composite design. Puddle welds are used for applications where the decking is a roof deck, overlain with insulation or when the concrete and steel do not interact and thus the concrete is just an overlay or filler. The designer of the particular structure makes that determination and it will be on the plans.

Yes, We are a manufacture of steel decking. I have never seen a job where studs did not take the place of puddle welding. It's a good idea to always get the EOR to approve this though.