Bevel Up versus Bevel Down
In general, I use a chisel with the bevel down for roughing cuts. I control the depth of cut by raising or lowering the handle. Since the bevel-down orientation tends to resist digging in, I use it for excavating a mortise, initial horizontal chiselling to a line, shaping concaves, paring in a tight spot, and removing waste.
For smoothing cuts, such as cutting flat or working with convex curves, I use the chisel held bevel up. Sometimes, you can use both types of bevel cuts interchangeably. For example, you can make feather cuts in mortising a hinge using the chisel with the bevel up or down. In many instances, both methods are needed to complete the job.
When chopping or paring vertically, face the bevel side toward the waste and begin the initial few cuts away from a scribed line. If you force a cutting edge on the line, the wedging action of the bevel will push back the scribed line.
Top) With the bevel down, there is less tendency for the chisel to dig in
Bottom) The bevel pushes the cutting edge away from the direction of the cut