This is startup-centric and depends heavily on the velocity of your project. For intrinsically difficult problems that evolve slowly or not at all (the most extreme example of this would be e.g. unsolved CS problems), source code is gold and its theft represents a huge blow to any competitive advantage a product might have had. Note that this is different from saying the source code itself doesn't evolve.
For problems whose difficulty relies rather on business concerns and which evolve rapidly then (the theft of) source code is nearly worthless.
For problems whose difficulty relies rather on business concerns and which evolve rapidly then (the theft of) source code is nearly worthless.