To clarify Rodney is talking about the built in BEC in the ESC, which is why he says it is good for planes that do NOT require a lot of current for the servos.

Hypersprint may be talking about using a seperate stand-alone BEC.

These typically CAN and DO handle higher power output requirements of higher torque servos.

I use standalone high power BECs with electric planes that have larger control surfaces and/or have a higher power ESC...

e.g. anything OVER 40 Amps.

Typically the higher the amp draw the less capacity available for the BEC's output to the servos which is why a standalone BEC is usually advised... and if you go higher, say to 80A esc's... these often do not have an on board BEC.