Would you recommend ChangeDetectionStrategy.OnPush as default changeDetection in Angular 2?

No, I wouldn't recommend that.

Angular 2 change detection is very fast. If you have a small project, I wouldn't bother using it.

If you have a large project, I would likely only use OnPush on certain "leaf" components -- leaf components that have view bindings that only depend on input properties. (A "leaf" component has no child components.)

Beware that OnPush can prevent child components from being automatically change detected, because if nothing caused the OnPush component to be change detected, none of its children will be checked either. Hence the reason I normally only use it on leaf components, to avoid this possible issue.

Also beware that if you use JavaScript reference types for input properties, OnPush will not detect changes you make to the properties of those reference types (e.g., if you add or remove an element from an array, or if you modify an object property's value.)

Especially for big project, the answer is YES and it is always recommended to add it as first thing when you create new components.

The reason is simple: to decrease the change detection process that it is a very expensive operation.

There are many ways of starting the detection when needed, maybe the most used is to trigger manually changeDetection() from the ChangeDetectorRef. Another way is using the async pipe in the view if you are waiting for a subscription value.

To add automatically the OnPush strategy when running the ng generate component command in the terminal, you just need to add the option in your angular.json at the schematics node:

...

    "schematics": {
        "@schematics/angular:component": {
            "changeDetection": "OnPush",
            "prefix": "app",
            "styleext": "scss"
        },
        "@schematics/angular:directive": {
            "prefix": "app"
        }
    }
...