Do You Really Need Plan Mode If You Already Use Agents Well?

A question that came up in a recent discussion made me pause.

If you already use Copilot Agents with clear instructions to plan first and not modify anything, what does Plan mode really add? Is it just convenience, or is there something fundamentally different going on?

It is a fair question, especially coming from people who already work deliberately with Copilot and have built their own disciplined workflows.

This post is not about defending Plan mode or arguing that one approach is better than another. It is about understanding where the difference actually lies, and when it matters.

This question builds on a series of earlier posts where I explored how GitHub Copilot’s different modes fit into AL development: Introduction to GitHub Copilot in VSCode for AL Development – think about IT

You Can Already Plan With an Agent

If you have spent some time working with Copilot, you quickly learn that behavior is largely shaped by instructions.

You can tell an Agent to:

analyze before acting
structure the problem first
avoid touching code
focus only on requirements and sequencing

With clear prompts, this works well. Some developers go further and create custom agents that consistently behave like a planning assistant.

From that perspective, Plan mode does not unlock a new capability. Planning was already possible.

So What Does Plan Mode Actually Add?

The difference is not about what Copilot can do, but about how strongly it is guided to do it.

Plan mode is opinionated by design. According to the official Visual Studio Code documentation, Plan mode introduces a dedicated planning phase where Copilot focuses on research, context gathering, and structuring the work before any implementation is considered.

The documentation explicitly describes Plan mode as generating a detailed plan that you can review and refine before deciding whether execution should happen at all.
https://code.visualstudio.com/docs/copilot/chat/chat-planning

This means Plan mode actively resists drifting into solutioning. Even if your request is phrased loosely, the workflow pulls the conversation back toward thinking instead of doing.

With a regular Agent, even one with good instructions, that boundary is easier to cross accidentally.

Where Custom Agents Shine

Custom agents remain incredibly powerful.

They allow you to:

encode your own working style
reuse prompts across projects
combine planning with domain specific rules
adapt behavior over time

If you already have a strong mental model and consciously separate planning from implementation, a well designed Agent can absolutely replace Plan mode for you.

In that case, you are not missing out. You have simply externalized the discipline into your own setup.

I also shared practical experiences with Copilot Agent mode in a separate post: Copilot Agent in AL: Using It Well Without Losing Control – think about IT

Under the Hood: Why Plan Mode Feels Different

One reason Plan mode feels different is how it structures the workflow internally.

The built-in Plan agent in VS Code follows a clear sequence. It first gathers context and constraints, then produces a structured plan, and only after that offers a path toward execution. This behavior is documented as part of Copilot’s planning workflow.
https://code.visualstudio.com/docs/copilot/chat/chat-planning

The key point is that the plan itself becomes an explicit artifact. It is something you can read, question, refine, or even hand off before any changes are made.

Seen this way, Plan mode is not about adding intelligence. It is about making intent explicit and durable.

Where Plan Mode Still Helps

Where Plan mode helps me personally is not in capability, but in friction reduction.

There are moments where I want to deliberately slow down:

before starting a new feature
when refactoring something messy
when requirements are still fuzzy

Plan mode makes that pause explicit. I do not have to restate the boundary or keep correcting the conversation. The workflow enforces it for me.

That matters more than it sounds, especially when switching contexts or working under time pressure.

This Is Not About the Tool

The more I use Copilot, the clearer this becomes.

The real distinction is not between Plan mode and Agent mode. It is between:

working reactively
working intentionally

If you already think in phases and consciously separate planning from implementation, the tool you use matters less. Plan mode simply nudges you in that direction by default.

If you do not, it can act as a useful guardrail.

I previously tried to capture this idea as a simple mental model for using Copilot intentionally: A Practical Mental Model for Using GitHub Copilot in AL Development – think about IT

Closing Thought

Plan mode is not magic, and it is not mandatory.

It is an opinionated way of slowing yourself down at the right moment. If you already do that through custom agents or personal discipline, you are probably using Copilot just as effectively.

In the end, the most important question is not which mode you use, but whether you are still thinking before you start building.

If you want a deeper explanation of how Plan mode works in practice, I covered that in a dedicated post: Copilot Plan Mode in AL: Clarifying Intent Before Writing Code – think about IT