Marginal Effects Interpretation I'm reading a paper that tries to estimate the following model:
$$y = \alpha x+\beta z+\gamma xz+\epsilon$$
where x,z are dummy variables and y isn't. 
The estimated coefficient of $\alpha$ is positive (0.02), and the sum of $\alpha+\gamma$ is negative (-0.01,insignificant). The writer examines the marginal effect of x, conditional on z and finds a positive (0.01, with significant of 90%). 
My question is what is the difference in interpretation of marginal effect VS. $\alpha+\gamma$?

The paper is "Terrorism and Voting: The Effect of Rocket Threat on Voting in Israeli Elections" by Anna Getmansky and Thomas Zeitzoff (link: https://www.zeitzoff.com/uploads/2/2/4/1/22413724/zeitzoff_getmank_rockets_main.pdf).
The marginal analysis is on page 11.
The paper computes the value of your coefficient $\gamma$ on its own with comparison to $\alpha +\gamma$1.

The interpretation in this context, would be that there is a limit of the returns to RightShare given the presence of observations existing contemporaneously with RightPM and InRange.



1. this of course assumes that $z=1$