What does it mean GPU doesn't like branches?

Question

GPGPU

Hello!
I've read that threads don't run in parallel when branching. As I understand it
, all processors are grouped into blocks, for example, 16 each, and all block processors work with the same instructions. Do branches affect processes within a block or between blocks too? Could you provide links to examples.

Answer 1

Branching means that the length of the sequence of instructions in different blocks will become different, therefore, some of the blocks will be idle at some point, waiting for the blocks that received more instructions to finish working.
And simple = losses.