Turning on the "planning ahead" strategy allows you to "plan" tasks and projects.
This can cause some confusion between the difference of scheduling and planning items.
Scheduling → Do date
Planning → Start and end date
Scheduling a task means you specify a specific day on which you want to complete the task.
Planning means you specify a time range in which you want to complete the task.
Both planning and scheduling help us narrow down the timeframe for when we want to complete a task. This is important for many reasons and helps us manage our time better and increase our changes of actually doing a task.
One more specific than the other
In Marvin when you schedule a task you are giving it a "do date". Which means you specify the exact day on which you want to do a task.
Planning on the other hand in Marvin basically assigns a start and an end date to a task. You can plan a task or project for a specific week or month.
This means that you don't need to do this task until the start of that period but you want to have this task finished no later then the end of that period.
A typical workflow pattern is to first commit to a task loosely and then schedule it to a specific day.
Or you can skip the step of scheduling tasks entirely and just plan your tasks for specific weeks and months and work from that list.
But you always move from loose commitment to a more firm commitment, not the other way around (which obviously does not make much sense).