In SMAC social engineering settings, Free Market Economics gives you the following bonuses:
+2 Economy
-5 Police
-3 Planet
This might seem a bit biased towards the negative side of things, but +2 Economy is actually a very powerful bonus, giving you +1 energy in every map square you are working. This bonus is very useful in times of peace, but in times of war, it is better to switch to Planned or Green economics, because the Police penalty makes it hard to wage a war outside your own borders without causing drone riots, while the Planet penalty makes your more vulnerable to attacks by psi based units such as Mind Worms
The Morganites have Agenda: Free Market and will try to use it as much as possible, while the Gaians have Aversion: Free Market, and can never use it (a considerable disadvantage).