Is setting the pretokenise flag advisable?

There won't be tokens, because Espruino automatically converts them back to readable text before output - also the function you uploaded doesn't actually contain any reserved words :)

Try:

E.setFlags({pretokenise:1});
function test() {
  for(var i=0;i<10;i++) {
    print(i);
  }
}
dump();

This prints:

function test() {for(var i=0;i<10;i++){print(i);}}
E.setFlags({ "deepSleep": 0, "pretokenise": 1, "unsafeFlash": 0, "unsyncFiles": 0 });

You'll notice all the whitespace is gone - that happened inside Espruino rather than being anything the IDE did.

Also if you really want to dive around in the internals:

>trace(test)
#30[r1,l1] Function {
  #29[r1,l2] Name String [1 blocks] "\xFFcod"    #38[r1,l0] FlatString [3 blocks] "\xA7(\xACi=0;i<10;i\x98){print(i);}"
  #22[r1,l2] Name String [1 blocks] "\xFFlin"= int 3
}

So the function code is now "\xA7(\xACi=0;i<10;i\x98){print(i);}" - so you can see for/var/++ have been replaced by character codes>127.

Just as a quick test:

E.setFlags({pretokenise:0});
function test() {
  var t = getTime();
  for(var i=0;i<10;i++) {    
    for(var j=0;j<500;j++) { /* This is a big comment in my code */ };
  }
  print(getTime()-t,process.memory().usage);
}
test();
E.setFlags({pretokenise:1});
function test() {
  var t = getTime();
  for(var i=0;i<10;i++) {
    for(var j=0;j<500;j++) { /* This is a big comment in my code */ };
  }
  print(getTime()-t,process.memory().usage);
}
test();
// gives
0.79599380493 51  // off
0.70184040069 47 // on

So in something like that you're about 10% faster and you saved a few variables too