The different types of optimizations change your board in order to reduce the total trace length and via count.

Arguments:

debumpify | Looks for U-shaped traces that can be shortened or eliminated.
unjaggy | Looks for corners which could be flipped to eliminate one or more corners (i.e. jaggy lines become simpler).
simple | Removing uneeded vias, replacing two or more trace segments in a row with a single segment. This is usually performed automatically after other optimizations.
vianudge | Looks for vias where all traces leave in the same direction. Tries to move via in that direction to eliminate one of the traces (and thus a corner).
viatrim | Looks for traces that go from via to via, where moving that trace to a different layer eliminates one or both vias.
orthopull | Looks for chains of traces all going in one direction, with more traces orthogonal on one side than on the other. Moves the chain in that direction, causing a net reduction in trace length, possibly eliminating traces and/or corners.
splitlines | Looks for lines that pass through vias, pins, or pads, and splits them into separate lines so they can be managed separately.
auto | Performs the above options, repeating until no further optimizations can be made.
miter | Replaces 90 degree corners with a pair of 45 degree corners, to reduce RF losses and trace length.