The IART position is that a two (2) piece stringing is the preferred format. Following is brief explanation of this position.
Two (2) piece stringing from the center out distributes stress in the racquet more uniformly. This is important when stringing a racquet that is well used or abused. Typically a new racquet can tolerate this stress but even a new racquet can be damaged internally.
Two (2) piece stringing is easier to handle. Typically the main string will be a separate piece therefore shorter than one piece for the whole racquet. With hybrid formats so popular the use of one piece of string is being diminished.
Two (2) piece stringing can, and in the position of IART, be used on racquets even though the main string may end at the top, which is referred to as a "natural one piece". This, again, is stress related.
Two (2) piece stringing should have the cross string started at the top of the racquet.
Two (2) piece stringing is consistent.
Two (2) piece stringing is straight forward and "simple".