Fraacta bring a nano pulsar with all profiles, a nice bonus for an AD trooper. With a combi rifle in most profiles with an option of a Boarding Shotgun or a Spitfire for additional Special Weapons Cost. They can also purchase an EI Assault Hacking Device at the usual SWC cost. Along with a pistol, knife, and CC 14 round out their profile. This puts them firmly in an assault role killing lightly armored troops and depleting the enemy order pool or support structure where it is vulnerable. Fraacta also have Courage to stay in firing positions when needed.
The Fraacta Transmutation, a skill that means that upon taking their first wound the trooper acts with a new profile. Unlike most similar troopers, this means that they actually get harder to kill after taking a wound, if albeit at the loss of some PH and MOV.
Since you have an additional wound on the profile it is possible to drop a Fraacta into a position where she might take a single ARO without going unconscious. Fraacta also work well walking onto the table where they are out of enemy LoF but can cover a short fire lane, then go into Supression Fire to force the opponent to dig them out before moving further up the board.
Never forget your nanopulser, as it is sometimes better than shooting and can be used for Intuitive Attack.
Fraacta work quite well in pairs. Most opponents, after suffering a first turn Fraacta attack, will assume the AD portion of your list is done and leave themselves vulnerable to the second trooper waiting overhead.
Knowing that AD is likely is the best way to defend against a Fraacta. Look for combat groups of only nine models, or large amounts of missing points in the enemy force. If there is an EVO repeater it is always worth assuming there will be at least one AD trooper inbound.
Unlike other AD troopers, it is not enough to have a single ARO waiting. You will want multiple, or high damage AROs to prevent them from striking at your lighter troops. This is of course easier to do when you have first turn, but even after the Fraacta has dropped, try to put a trooper into Suppression fire or good range bands in the area the Fraacta will have to move through.
Fraacta are vulnerable in assault and even a mediocre CC specialist will probably remove them.
As stated above Fraacta do work well in pairs, but as a base covering piece, most lists can benefit from one. Should the enemy give you a good opertunity such as a weak back flank or an obvious and vulnerable Lt. then the Fraacta can try to capitalize. If not, they can still be used to threaten difficult enemy pieces.
Fraacta are especially nice in missions such as Supremacy or Transmission Matrix. The cost a lot of points are are hard to remove with a single ARO meaning if you are going second, you can drop them in, or run them on board somewhere that your enemy has fewer points and steal a quadrant.
If you need a hacker there are many better options, but the Assault hacker has a ton of offensive tech along with counting as a specialist, making her a good choice in objective missions that require you to move further up field.
The Fraacta are AD:Combat Jump troopers and as such are rarely, if ever deployed on the field. When arriving on board always remember that you can choose to downgrade your AD:Combat Jump to AD:Parachutist and walk on via the board edge to avoid AROs
Active Turn Role
The Fraacta wants to kill low armor enemy targets or set up multiple troopers in her Nanopulsar or Boarding Shotgun templates. Drones are particularly vulnerable to this if you can attack them from behind as the Change Facing at an additional -3. Fraacta should either remove problem pieces (such as long range shooters or specialists) or target the order pool, but probably not both. They are order intensive high risk investments. Because you are likely to lose them it can be worth leaving them out to secure another few kills, but a Fraacta that has the orders to step out of LoF and go into supression fire will be a pain for your opponent.
In ARO the Fraacta is like most other troopers with the exception of her extra wound. This can allow her to more reliably take a normal roll and use her Nanopulsar, or target non-active link members and hope to survive the barrage of enemy fire. It is worth remembering that her PH goes from 12 to 10 once she has taken a wound so dodging is usually only going to work before she has taken hits.