1. A computer-implemented method for optimizing placement of virtual machines on physical hosts of a computer system, the method comprising: getting current conditions of the computer system; getting aggressiveness policies that indicate to change at least one aggressiveness setting depending on system conditions comprising: number of migration failures in the past, number of network connections for a physical host, number of packets dropped on a network connection, number of deployments in the past, the total number of virtual machines in the system, total number of hosts in the system, wherein the aggressiveness settings comprise: a maximum number of migrations per host per hour, a maximum number of migrations per cloud per hour, a maximum number of concurrent migrations per host and a maximum number of concurrent migrations per cloud; evaluating the aggressiveness policies using the current conditions to update the aggressiveness settings by a. getting the current date and time; b. when there are policies for the current date and time, applying the aggressiveness policies for the current date and time to update the aggressiveness settings; sending the updated aggressiveness settings to a system optimizer for dynamically changing aggressiveness of loading virtual machines on the physical hosts with the updated aggressiveness settings; and dynamically changing aggressiveness of loading virtual machines on the physical hosts with the updated aggressiveness settings.