What do the different dumping filter preferences mean?

These options capture the following packets:

No dumping - just what it says. No log file is written.
Keep everything - All intercepted traffic is written to the log file.
Data only - Only packets containing data are written to the log file; empty, "I'm here," traffic is ignored, but any packets with weak initialization vectors (IVs) will be logged.
Weak frames only - only packets with weak initialization vectors will be written to the log file.

If you aren't interested in doing anything with the data, Weak frames only is probably the best choice.

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