When you are planning your flexfields, you should consider the following questions and their corresponding decisions:
Do you want to capture information that is not otherwise captured by the window or page? If yes, you define this descriptive flexfield. If no, you need not define this descriptive flexfield at all.
Do you want to capture the same information every time, regardless of what other data appears? If yes, you need to define global segments.
Do you want to capture certain information sometimes, depending on what other data appears in the form or page? If yes, you need to define context-sensitive segments.
If you want context-sensitive segments, do you want to have the form automatically determine which descriptive flexfield structure to display based on the value of a field somewhere on the form? If yes, you need to define a reference field (note that some descriptive flexfields do not provide reference fields).
If you want context-sensitive segments, do you want to have the user determine which descriptive flexfield structure to display by choosing a value in a field inside the pop-up window? If yes, you need to define a context field.
How do you want to break down reporting on your descriptive flexfield data? If you want to report on your data by certain criteria or sub-entities, such as account number or project or region, you may want to consider making that sub-entity a distinct segment, rather than combining it with another sub-entity, so that you can categorize and report on smaller discrete units of information.
How often does your organization change? This would affect how you set up your values. For example, if you disable old values for a segment and enable new ones frequently, you would "use up" values quickly. You would therefore want to set up your value set so that you can have more available values than you would otherwise.
Do you want to require a value for each segment?
Do you want to use Flexfield Value Security with your descriptive flexfield?
You should decide on the number, order and length of your segments for each structure. You must also choose how to validate each segment.