Great questions—let’s unpack this so you can pick the right tool for the job without worrying about unnecessary overhead.

Performance Differences: None at All #

First things first: there is no performance gap between <ng-container> and <ng-template>. Here’s why:

• <ng-container> is essentially a syntactic sugar wrapper that Angular compiles directly into <ng-template> under the hood when paired with structural directives (like *ngIf or *ngFor). It never gets rendered as a real DOM element, just like <ng-template>.
• As you noted, Angular de-sugars syntax like <div *ngFor="let person of persons"></div> into a <ng-template> structure. If you wrote <ng-container *ngFor="let person of persons"><div></div></ng-container>, the compiler would do almost the exact same work—converting the *ngFor into the underlying <ng-template ngFor> binding, with no extra DOM nodes or runtime cost added.

In short: Both are handled identically by Angular’s compiler and runtime. No performance tradeoffs here.

How to Choose Between Them #

The decision comes down to your use case, not performance:

Use <ng-container> when: #

• You need a logical grouping for elements without adding extra DOM nodes. For example, if you want to apply a single *ngIf to multiple elements without wrapping them in a <div> or <span>:

  <ng-container *ngIf="user.isAuthenticated">
    <h2>Welcome back, {{user.name}}!</h2>
    <nav>
      <a href="/profile">Profile</a>
      <a href="/settings">Settings</a>
    </nav>
  </ng-container>
  

• You want to use the convenient * syntax for structural directives (like *ngFor, *ngIf) without tying them to a real DOM element.

Use <ng-template> when: #

• You need to define a reusable template fragment that you can render dynamically with ngTemplateOutlet. For example, creating a loading state that you can reuse across components:

  <ng-template #loadingState>
    <div class="spinner">Loading content...</div>
  </ng-template>
  
  <!-- Render the template when data is loading -->
  <div *ngIf="data; else loadingState">
    {{data.content}}
  </div>
  

• You need to work with the raw, un-sugared structural directive syntax (e.g., building custom directives that interact with templates, or using advanced features like let- context variables directly). For example:

  <ng-template ngFor let-person [ngForOf]="users" let-index="index">
    <div>{{index + 1}}: {{person.name}}</div>
  </ng-template>
  

• You want to define a template that won’t render automatically (since <ng-template> is never rendered by default—you have to explicitly reference it with an outlet or directive).

Quick Recap #

• Performance: No difference whatsoever. Both are "invisible" to the final DOM and handled the same by Angular.
• <ng-container>: Your go-to for grouping elements with structural directives without extra DOM noise.
• <ng-template>: Use for reusable, manually-controlled template fragments or advanced directive work.

内容的提问来源于stack exchange，提问作者Yashwardhan Pauranik