SNATCH BLOCKS AND THEIR USE
So ideally the line of pull on a winch should always be straight ahead as that ensures that the winch wire does not gather on one side of the drum and naturally spools up neat and tidy.
The image below shows snatch blocks and their relative ratios
1:1 or direct/redirected pull.
Using a snatch block to redirect the pull direction is useful if you have another vehicle to anchor to but it is at 90 degrees to you. Despite the redirection of the winch line you are still getting a direct 1:1 pull.
2:1 Ratio
Here you are stuck deep in mud upto the axles and you need to make sure that you are not going to cook the winch.
By using this set up you make the winch work less hard to pull a given weight but you also half the speed in with which your winch retrieves its cable.
Effectively the force of the pull is halved between the two cable runs.
3:1 Ratio
Here the cable is fed through two snatch blocks so the force is shared between 3 lengths of cable effectively dividing the force by 3 hence 3:1.
This in turn also reduces the winch speed of cable retrieval to one third it's normal speed.
You can also use snatch blocks to winch yourself backwards with a forward winch, winch yourself sideways to clear obstructions plus all other manner of things.