[gkop]

You don't typically.

One case where you would View Source in addition to using Dev Tools is debugging how the browser is massaging your source HTML into the DOM, for example by inserting missing <tbody> elements. Validating your HTML mostly addresses this (I'm actually not sure about the <tbody> example, I would hope the validator at least issues a warning), but isn't something you necessarily want or can do with, for example, user-uploaded HTML snippets.

[mullsork]

True, though I guess using some HTML validation could improve that. Not sure if <tbody> is mandatory but I think I've seen some tool complain about its absence.