Why should we bake bare PCB?

I want to desolder a tiny surface mount button from the motherboard of a phone. There are a lot of similarly tiny components surrounding it that I do not want to damage with heat from the soldering iron. Can I use aluminium foil in lieu of kapton tape to protect these components?

My PCBA supplier use molex connectors on the samples order. What are they? What does they feature?

I know the paste mask layer is also called the stencil layer. It’s only used for assembly. I want to know if the paste mask layer (both top and bottom layer) is necessary for through hole components. For SMD components I know the paste mask layer is required to solder the components. Is it necessary for through hole components?