A new targeting option enables Heli to seek and pursue the Bloons automatically.
Pursuit is the second upgrade on the first path for the Heli Pilot in both BTD5 Mobile and BTD6. It gives the Heli Pilot a new target priority: Pursuit. Pursuit target priority allows the Heli Pilot to follow bloons that are the closest to the exit, equivalent to the target "first". This is automatic, no touch is needed. So it can be really useful if you don't want to be busy controlling it.
In BTD5 Mobile and BMC, the current setting of the Heli Pilot would need to be changed to activate Pursuit mode; in BTD Battles Mobile, it automatically changes to Pursuit Mode upon purchase of the upgrade. In the BTD5 generation, Pursuit would typically be around 50 pixels away from the most first bloon on at any angle from the point of the targeted bloon, which typically rendered Razor Rotors less reliable on this setting. In BTD6, the Pursuit targeting has improved so that it will follow along the track as close as possible to the front of the bloon, compacting with other Heli Pilots on Pursuit in the order of whichever Heli Pilot went to Pursuit first.
Pursuit is primarily designed as a hands-free upgrade for letting the Heli Pilot automatically target bloons, which in turn may allow for less micromanagement of the Heli Pilot. In terms of practicality, it is mostly used strategically for defenses that include Banana Farms, as picking up bananas is often disturbed by manual micromanagement of the Heli Pilot.
Unless hands-free defense is necessary for a special purpose, try to avoid purchasing this upgrade, as normal Heli Pilot micromanagement is usually offers more efficient control over the Heli Pilot.
It is not recommended to use Pursuit targeting in combination with the Razor Rotors upgrade, as a Razor Rotors on Pursuit targeting tends to underperform versus Lead Bloons, even with the slight rotor range buff.
The Pursuit upgrade can be used in combination with Downdraft to effectively blow back the Ceramics spawned from early MOABs directly after destroying them.
In the BTD5 series, the Pursuit upgrade was formerly the only upgrade that gives a tower a new targeting option. When the Monkey Sub was added to the mobile tower roster of BTD5, it too got a targeting option granted to it by an upgrade.