As mentioned in my other post, I'm preping to run a new dresden game and still struggling with how to effectively use some game concepts.  I'm struggling with how Consequences are actually run during encounters.  What is the actual effect other than the description?

Are they a blanket negative shift to skill rolls for as long as it lasts? If so how much?

What about stacking consequences?  If you have a mild and server is the negative shift cumulative?

I'm struggling with how to make consequences have actual in game consequences beyond the description and could use some examples of how GMs are using it.

I'm gearing up to run my first Dresden Game an I'm still a bit fuzzy on scene or situation aspects and how best to use them in a game.

It seems the systems wants to keep it in the realm of tagging to use an aspect free the first time and using Fate Points each time after that but I'm not sure I'm clear on how that's really suppose to work.

Lets take the following scene as an example:

The players Ron and Anna are entering an abandoned tenement building with bricked over windows and no lighting so the building has the PITCH BLACK scene aspect.  They suddenly realize they were followed by Frank who is standing in the doorway behind them lite from behind by the streetlights.  Frank has a SILHOUETTED temporary aspect while he stands in the doorway.

So my mind goes a bit fuzzy on how different requests would work out in this exchange and it seems like it would be too easy to drain all the characters fate points just trying to use the natural environments.

Say I want to give Ron or Anna an Alertness roll to avoid an ambush from Frank.  Seems straight forward, they tagg the SILHOUETED temp aspect and get a bonus on the defense roll.  What I don't understand is let's say they don't get ambushed in exchanges after that they'd have to spend a fate point to add to their defense for PITCH BLACK?  I don't quiet get that though and why are they spending fate points for that.  Alternatively I could say they don't have to use Fate Points and treat like a compel on Frank but what are the effects of a compel?

Fate points are straight forward but I don't see any specific draw back for compel, is a -2 shifts a good rule of thumb for specific compels like firing a gun at someone hidden in PITCH BLACK space?

Say nobody sees anybody and Anna and Ron are hiding while Frank is in the doorway.  Ron wants to try to use Alertness to make out Franks face and figure out who the figure SILHOUTETED in the doorway is.  Sounds reasonable to give Frank a compel for since Frank is only outlined but again what do I use?  -1 shift,-2?  Something else?

Say Ron and Anna just take cover, waiting for their friend to swoop in and resume them and Frank starts shooting away from the doorway.  Do they have to spend Fate Points every round to keep the bonus from the PITCH BLACK.

There are a lot of situations where it seems like we'd just be bleeding off Fate Points but maybe in play it doesn't work out like that.  Any advice or thoughts on how I might clear this up in my mind?