If you do not want to get the people who put their lives on the line to defend our country killed needlessly by warning the enemy that they are coming, you sometimes need to give them the authority to at without signalling our intentions through a parliamentary vote.
The cartoonist Cummings made the point like this during the Falklands war
Hence it is spectacularly daft that Jeremy Corbyn has now said he want a "war powers act" which would stop ministers deploying British special forces without parliamentary approval.
Iain Martin put it very well here,
"Special forces that require a parliamentary vote before they take out an Islamist bunker won’t be very special or forceful. As someone on Twitter put it: why not just send ISIS a postcard ahead of each operation? In suggesting a Commons vote on SAS deployment it is almost as though Corbyn doesn’t want the West to have any tools to defend itself. Funny that."