Layers convert to smart object

[MahaB82A]

Is there any reason of converting both layes together into smart object? Video link is given. If we retain individual layer and convert individual layer into smart object, later it is easy to choose color of the background layer which we like.  

Time 0.14

Horror Ripple Text Effect

[c.pfaffenbichler]

Not all Filters process transparency. 

And what if the background is not just a plain color?