Understanding the high upside stash

I have been watching as the FF experts identify players that are coming back from injury or are getting more playing time due to injuries to players in front of them. These player last are kind of tagged as high upside bench stashes that have the potential to have a large impact on your fantasy season. What I rarely see is anyone saying to start them. As we enter week 13 heading toward playoffs, at what point do we expect stashes to move up higher in the rankings and be recommended as a start? An example would be a Dede Westbrook or Corey Coleman where they were labeled as must adds but have rarely been recommended as a start even in what are considered favorable matchups. Just trying to understand what to do with these types going into the playoffs and are they worth keeping vs a typical handcuff for a high value RB1/2. Thoughts?