// BAD: Allocates every frame
void Update() {
    string label = "Score: " + score.ToString();
    var enemies = FindObjectsOfType<Enemy>();
    var filtered = enemies.Where(e => e.IsAlive).ToList();
}

// GOOD: Zero allocations in Update
private StringBuilder _sb = new StringBuilder(32);
private List<Enemy> _enemyCache = new List<Enemy>();
private Enemy[] _enemyArray;

void Start() {
    _enemyArray = FindObjectsOfType<Enemy>();
}

void Update() {
    _sb.Clear();
    _sb.Append("Score: ");
    _sb.Append(score);
}

// Flag these patterns in code review:
Camera.main                          // Calls FindWithTag internally
GameObject.Find("name")             // Linear search every call
GetComponent<T>() in Update         // Cache the result
new List<T>() in Update             // Allocates on heap
string + string in Update           // Creates new string objects
foreach on non-List collections     // Enumerator allocation
LINQ queries (.Where, .Select)      // Multiple allocations
Boxing (int -> object)              // Heap allocation
delegate/lambda in hot paths        // Closure allocation

// BAD: Empty Update still has overhead
void Update() { }

// BAD: Logic that doesn't need per-frame execution
void Update() {
    SavePlayerPrefs();  // Should be event-driven
}

// GOOD: Use events, coroutines, or InvokeRepeating for non-per-frame logic
void OnScoreChanged(int newScore) {
    UpdateScoreUI(newScore);
}

// BAD: Camera.main uses FindWithTag internally
void Update() {
    transform.LookAt(Camera.main.transform);
}

// GOOD: Cache the reference
private Transform _cameraTransform;

void Start() {
    _cameraTransform = Camera.main.transform;
}

void Update() {
    transform.LookAt(_cameraTransform);
}

// BAD: Expensive search every frame
void Update() {
    var player = GameObject.FindWithTag("Player");
    var rb = player.GetComponent<Rigidbody>();
}

// GOOD: Cache in Awake/Start or use dependency injection
private Rigidbody _playerRb;

void Awake() {
    _playerRb = GameObject.FindWithTag("Player").GetComponent<Rigidbody>();
}

undefined

Use device-side profiling to validate that code review findings translate to real performance improvements.