WIC-1T One Port Serial Cisco T1 Card Explained

[hokibacsi1]

Could someone plase explain it to me what are the major differences between a WIC-1T port and one NM-4A/S or NM-8A/S Four Port Async/Sync Network Module?

I am a donkey and just by looking at the datasheet for me it is unclear why a WIC-1T is better, since it is just a serial port like NM-4AS.

Naively I think that the NM-4A/S or NM-8A/S ports can be used only between CISCO devices to link them in back-to-back config, and the WIC-1T is for having an other device connected to it --like a modem...