When you setup a carrier in transportation management there is a flag called use carrier which in effect enables or disables the carrier to make it active to use.  There might be times when you don’t want to use a carrier after you set them up temporarily or long term so you could use this flag. Keep in mind the communication to users as it might be confusing if the carrier is deactivated after being setup.

Here is a quick walk through of the effect of the user carrier flag on the shipping carrier.

Cheers

Lachlan