4-Axis Robots and WJNT

Ok. So I inherited some robot code, on a few M410s. The Original Programmer has some linear moves, that he sometimes uses a WJNT with and sometimes not. It's the exact same path, and point, and speed, etc. the only difference is the WJNT see below:

  #:  IF (some status is met) THEN ;
  #:L PR[99:VARPOS] 1000mm/sec CR25 Wjnt    ;
  #:  ELSE ;
  #:L PR[99:VARPOS] 1000mm/sec CR25    ;
  #:  ENDIF ;

The Question is, with these being 410s (4-Axis robots) what really is the difference that a WJNT would do to the move, and why WOULDN'T you ALWAYS use a WJNT?

From what I'm told, this may have been added because at one point J4 would execute this move during a certain case (Without WJNT) and would end up winding itself up and causing an axis limit error.

Is there any reason you wouldn't want to use a WJNT move? specifically with a 4 axis robot?