How to have rounded edges during modeling?

I’m not meaning to press on Smooth or to use a Subsurf modifier; I mean just to see the edges rounded while modeling.
Like I see sometimes in the tutorials…

Like this

Enable the option to have the subsurf modifier on in Edit Mode. It’s not really recommended to model with this on.

Oh cool thanks, ok! Yes I imagine the why it’s not recommended but I wanted to activate it just to see better the flow of the topology