unwindonsignal variable question

[Phil Muldoon]

Setting this to "on" fixes the most problematic aspects of gnats pr 
2495. (This is where an exception is raised in a C++ function executed 
by inferior function call, and no in-frame exception handler results in 
a sigabrt being delivered to the inferior).

As this is a very useful flag, and it only seems to apply in inferior 
function calls, I am curious why it appears to default as "off", 
requiring the user to perform:

set unwindonsignal on

(I'm not advocating changing it, just curious if there is a  particular 
reason for it to be this way). And also, if there would be known 
side-effects to having it to default as on.

Regards

Phil