Squad Action (UFO2000)
Use of roles on Offensive/Defensive strategies
Some or all of these elements can be found on offensive/defensive strategies. Even on a frontal attack the division between Assault/Support elements will occur naturally as some units will stop to fire while the others advance. The same might happen on a purely defensive strategy where an opportunity for a counter attack can show up and the advancing units will form an Assault element.
Tactical reserves
A deciding factor on fights is the application of a tactical reserve. Usually it is made of idle units that switch to a different role, either to give the Assault element the extra humpth to break through a defense or reinforce any other sector. Reserve units thus give some versatility to the squad as a last resort measure or to respond to a surprise enemy move.
When all hell breaks loose
To bring back this chapter to its beginning, a squad's subdivision can either be done right from the beginning, where each soldier is assigned and deployed as a member of an Assault/Support/Security team or the division can happen naturally on the battlefield. Usually there's a lot of switching between roles as the battle takes place, i.e., a Support element might find itself suddenly switching to a Security role when the enemy manages to break through and threaten your rear. But this switching of roles can bring several problems of its own, if the units are too specialized. If there's a team for Support, with lighter armor, low TUs and area weapons, it can find itself in trouble while trying to stop an enemy that has more armor, more TUs and close range weapons. On the other hand, if all of your soldiers have power suits it can be a waste of points that could be used on more units/weapons if the support units are never fired upon the entire game. This switching also applies to a specialty: if all your scouts are dead at the middle of the game you will need to use other units to find the enemy. Always be prepared to improvise but at the same time know what to expect from your units.