Why the battlecruisers were never sent out alone

What if the British misread the intelligence and sent only the battlecruisers out?

They would have to withdraw. In the actual British deployment, the Grand Fleet also sailed to support them.

Unsupported battlecruisers would have to run away from the German battle fleet. British planners understood the German aim of isolating and overwhelming part of the Royal Navy, so they sent the Grand Fleet in support. The speed of its deployment determined when the forces could combine. Even destroying the battlecruiser force alone would not necessarily give Germany the change in the overall balance it needed.