How to have rounded edges during modeling?

Support Basics & Interface
1

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 https://www.safaribooksonline.com/library/view/learning-blender-a/9780133886283/graphics/08fig05.jpg

2

Enable the option to have the subsurf modifier on in Edit Mode. It’s not really recommended to model with this on. http://blender-manual-i18n.readthedocs.io/ja/latest/modifiers/generate/subsurf.html#edit-cage

3

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