This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
The main application for Green fuse in rocketry is as an auxuliary delay
when a timer is not available and Thermalite is too fast burning. Green
Visco fuse burns about 30 seconds per foot.
"Green" fuse isn't reliable, and unless electrically ignited via remote
control (difficult) isn't legal. To use fuse and a match is a violation of
the safety code, and most state local regulations.
email@example.com (Buzz McDermott) adds to the above:
The most common way to use 'green' fuse or Jetex wick to ignite a model
rocket motor is to cut a fair length, insert it in the motor, light it
with a match, and RUN!. As Bob stated, it's against EVERYONE's safety
code to do that. The answer to 'why' is simple. Once you light the fuse
you've lost all control over launching the rocket. If a breeze kicks it
over just before ignition you end up launching a land shark. You can't
stop the launch if you notice a plane come out of nowhere and fly right
overhead. You can't stop the launch if a little kid comes out of nowhere
and runs up to your rocket. ...on top of all this, the stuff just
really work all that well for rocket ignition...