The welding symbol provides the "minimum" welding requirements to meet the need to transfer the applied load from one member to the connecting member. The intermittent fillet weld is often used where the loads are not high and minimal weld is needed. The designer has to size the weld based on the load, but also based on the minimum weld size dictated by the thickness of the base metal. The welds are preferably spaced "uniformly" along the length of the joint to minimize distortion, i.e., buckling, etc. So, one can think of the intermittent fillet weld as being the minimum amount of weld needed to get the job done.
If the welder lays out the welds as suggested by Brent, he hooks the tape on the end of the member and marks out the weld length, followed by the unwelded space, weld length, unwelded space, .... the required weld will be sufficient to meet the needs of the design.
If the welder makes the weld slightly longer, no harm, no fowl other than lost profit for the employer. Some welders are fastidious about the weld size and the weld length, others, let's say they are not as careful. If the welds are too big, the lengths too long, the strength requirement is met, but from a management perspective, it is a profit eating problem. In the case of architecturally exposed steel, it can be a workmanship and appearance issue.
The intermittent fillet weld symbol shouldn’t be used if the weld must be located precisely, it was never intended for that purpose.
I once encountered an inspector that insisted the welds be located within 1/16-inch of the ideal location and the weld lengths couldn’t be more that 1/16-inch longer than specified. The welders would spend hours with their end grinders and carbide burr removing the excess weld. If the welds were too small or too short, the sky would come crashing down. That inspector was a fool and he cost his employer many thousands of dollars because the application didn’t warrant the degree of precision he demanded. I challenged him and asked what was the basis of his unreasonable demands. His response was “That’s what I want.” He and his ego were sent packing when upper management got wind of what was going on.
The inspector should understand the impact of being overzealous. If the welds are too short, too small, there is an impact on the safety of the structure. If the welds are too big or too long, there is an impact on the profit margin. Shop supervision has a responsibility to ensure the employer makes a profit. The inspector has a responsibility to ensure a product is shipped that meets the requirements of the drawings. Under ideal circumstances, there is communication between the different parties and problems and short-comings can be identified and solved. Under unfavorable conditions, the different parties are in conflict, each “protecting” their own self-interest. The employer usually is the loser in the latter case.
That's my story and I'm sticking to it.
Al