Removable glue for LEGO models
Officially, LEGO Group doesn't recommend any adhesive on the toys. It can lead to corrosion or warping chemically, warping physically (the glue puts pressure on the pieces), and the removal of the adhesive also carries these risks. Plus, you'd be killing not only the the monetary value of the set, but the ability of those pieces to be active stimuli for creativity and motor skills. 

The LEGO Movie clearly shows that using glue on the toys is what the villain does.