what are the advantages/disadvantages of one?

 

I'm assuming you're talking about a fuel cut switch.
There are NO disadvantages in having one (unless you somehow completely screw up the wiring ).
Advantages... let's just say that for many varied reasons, your car WILL flood. Having the fuel cut switch could be the difference between driving home, and walking home.

Fuel Cut Switch info.

There is a 6-point connector under the dash right by the steering colum (to see it, you basically have to put your head right underneath the steering column, as far back as you can go). Cut the middle wire, it is black with a white stripe. Make sure you leave enough wire hanging out so you can splice another wire onto both ends. Get a switch with two prongs on the end. Connect a length of wire onto one prong and splice to one of the ends of the cut wire, do the same with the other prong and another peice of wire. That should do it for you. To use it just flip the switch and let it stall out on its own. Then to start it, start cranking the engine then flip the switch while still cranking the engine, she should start right up. You might have to experiment a bit, but you'll get the hang of it.

Where to put the switch:
That's up to you. You can use this switch as a theft deterent as well, so you could 'hide' the switch. I think most people put it under the steering column.

 

It's got a yellow plug, so you can't miss it. You don't need to do this unless you have a serious, repetitive flooding problem. For most people this isn't a common occurence. If the car floods, turn the switch off, press the gas pedal to the floor and hold it, crank the engine for 5-10 seconds (no more, you'll cook the starter) and then flip the switch on as you continue to crank. It should fire right up.

 

On stock S5's - WOT while cranking cuts the fuel pump.

 

there is a beneift to the fuel cut switch. if you need to work on your fuel system (ie open it up)the switch is a great thing to have becauseu can just shut it off, let the engine starve then do whatever you have to do. no worrying about fuel spray when you open a line

 

There will still be some pressure in the return line no matter how many times you crank it with no fuel heading towards the motor...don't ask how I know...