Why are common mode filters / chokes necessary?

In which locations can common mode filters (common mode chokes) be effectively used as EMC countermeasure components?

It seems that there is no mark indicating the winding direction (polarity) on common mode filters / chokes. If their directions are different when they are mounted, would the properties change?

Are there any problems in mounting common mode filters / chokes in GND-signal lines?

Can common mode filters / chokes be used on the primary side of a power supply? Can common mode filters / chokes be used in AC lines?

Are there any problems in mounting common mode filters / chokes for signal lines?

Do common mode filters / chokes generate heat?

Where can the reflow conditions of TDK’s common mode filters (common mode chokes) be confirmed?

Please provide instructions on how to select common mode filters (common mode chokes).

TDK’s common mode filters (common mode chokes) include multilayer products, thin-film products, and wire wound products, but what are their differences (features)?

Where can I confirm the weight of common mode filters (common mode chokes)?

Where can I view a list of TDK’s common mode filters (common mode chokes)?