I am building a startup and I am pre product. Imagine the velocity at which the build is happening.
I was preparing a demo for a potential inital user for feedback. Demo was made in two days with just enough feature set to get the feel of the product, thanks to flutter + firebase.
At the last minute I somehow felt that the widgets in the screen weren't taking up enough space when the app is opened in a tablet. So to just be doubly sure, I added a Expanded widget at the top level. Triggered a debug run and everything seemed fine. Hence pushed to prod and went on for the demo.

As you have guessed, the demo flopped. Here are my learnings:

The Expanded widget is typically used within a Column or Row to indicate that its child should take up the remaining space in the main axis.

However, using Expanded requires its parent widget to have constraints to determine how much space should be allocated to the child. However, using Expanded requires its parent widget to have constraints to determine how much space should be allocated to the child. In some cases, especially when dealing with complex layouts or nested widgets, the absence of constraints can lead to errors or unexpected behavior, particularly in release builds where optimizations may differ.

It's important to note that while Expanded is a powerful tool for managing layout in Flutter, it's not always necessary and can sometimes be omitted depending on the specific requirements of your UI. It's always a good idea to simplify your layout and remove unnecessary widgets if they aren't contributing to the desired behavior or causing issues.

here are some scenarios where you might want to use or avoid using the Expanded widget in Flutter:

When to Use Expanded:

Flexible Layouts:
Use Expanded when you want a child widget to take up the available space along the main axis of a Row or Column. For example, if you have a list of items in a Column and you want one of the items to expand to fill the remaining space, you would wrap it with Expanded.

Column(
  children: [
    Text('Header'),
    Expanded(
      child: Container(color: Colors.blue),
    ),
    Text('Footer'),
  ],
)

Flexible Containers:
When you want a container to expand to fill the available space within its parent widget, you can use Expanded.

Row(
  children: [
    Container(color: Colors.red),
    Expanded(
      child: Container(color: Colors.blue),
    ),
    Container(color: Colors.green),
  ],
)

Flexible Sized Boxes:
Sometimes you might want a SizedBox to take up the available space within a parent widget. Wrapping it with Expanded can achieve this.

Column(
  children: [
    SizedBox(height: 20),
    Expanded(
      child: Container(color: Colors.blue),
    ),
    SizedBox(height: 20),
  ],
)

When Not to Use Expanded:

When Child Should Take Its Intrinsic Size:
If the child widget should only take its intrinsic size and not expand to fill available space, avoid using Expanded.

Row(
  children: [
    Container(width: 100, height: 100, color: Colors.blue),
    // No need for Expanded if the child should maintain its intrinsic size
    Container(width: 200, height: 100, color: Colors.red),
  ],
)

When Constraints Are Not Clear:
If the parent widget does not provide clear constraints, using Expanded might lead to layout issues. In such cases, consider using other widgets or reorganizing your layout.

Column(
  children: [
    // The parent Column does not provide constraints, so using Expanded here might lead to issues
    Expanded(
      child: Container(color: Colors.blue),
    ),
  ],
)

Single Child Layouts:
If you only have one child in a Row or Column and you want it to take up the available space, you might not need Expanded.

Column(
  children: [
    // Only one child, it will take up the available space by default
    Container(color: Colors.blue),
  ],
)

Remember, the decision to use Expanded depends on the specific layout requirements of your UI. Use it when you need a child to fill available space, and avoid it when you don't want the child to expand or when constraints are unclear.

Best Practices and Tips**

Use with Caution: While the Expanded widget can be a powerful tool for managing layout in Flutter, it should be used judiciously. Overusing Expanded can lead to complex and difficult-to-maintain layouts. Reserve its use for cases where you truly need a child widget to expand to fill available space.

Combine with Flex: The Expanded widget works hand in hand with Flex widgets like Row and Column. When using Expanded within a Row or Column, ensure that the mainAxisSize property of the parent is set to MainAxisSize.max. This allows the Expanded widget to expand to fill the available space along the main axis.

Avoid Nesting: Avoid nesting Expanded widgets within each other, as this can lead to unpredictable layout behavior. Instead, consider using a combination of Expanded and Flexible widgets within a Flex container to achieve more flexible layouts.

Test Across Devices: Always test your layouts across different devices and screen sizes, especially when using Expanded. While Expanded is great for filling available space, it's important to ensure that your layout remains responsive and looks good on all devices.

Optimize Performance: Be mindful of performance implications when using Expanded, especially in large and complex layouts. Overuse of Expanded can result in unnecessary widget rebuilding and layout recalculations, leading to performance issues. Keep your layout hierarchy as simple and efficient as possible.

it is fun to startup. if it goes by your plan, great. if not, you can always write about it. either way it is a win.

you can expect more about startups, flutter and firebase from me. letting you know just in case you are wondering to follow or not.

cheers!