I don't understand the whole check decide thing.  Every time I hear this I hear "I don't have a plan, hope my opponent doesn't bet" between the lines.  

It doesn't make sense to me.  What are people making the supposed decision based on?  Timing?  Bet sizing?  What else is there?  The cards are known.  There are only forty odd cards left on the next street depending on the game type.  It's not all that hard to have a plan for forty cards.  And making decisions on one street without anticipating all actions from the opponent and having a plan for all cards for at least the next street -- then I'd say there is a fairly significant hole in the game strategy.  What am I missing here?

Check decide seems like a mistake to me.  Can someone pls help me understand when this could be a good play?