What are the benefits of Portable gas leak detector?

You can detect portable gas leaks.

It can tell you if the leak is in a particular cabinet  and or, can narrow down the search along a pipe or coil. Depends on how good the detector is. The one I have now is 100 times better then the one I had in the 90's.

you don't have to spray soapy water  but  once you know there is a leak to pin piont the exact spot of the leak you have tp use soapy water 

Chances of you having a gas leak are very small and if you ever do you can usually narrow it down by smell  .Then you can spray a soapy water mixture on joints to find the leak as well .So not really necessary to buy the detector until you need it.

None at all if you don't have gas laid on.

It detects gas and is portable. What else?

To know if there is a gas leak 

You can carry it around with you