[Samba] Store plaintext passwords

[Felipe_G0NZÁLEZ_SANTIAG0]

I'm in doubt about the 'Store plaintext passwords' option. What it does mean? 
Are the passwords sending in cleartext on the network? Is posible to catch and see the passwords ? 

What's the best practice about this option? 

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Ing. Felipe_ González_Santiago 
Universidad_de_las_Ciencias_Informáticas 
Centro_de_Software_Libre 
"Remind yourself that you cannot fail at being yourself" 
Wayne Dyer