Without user intervention, Vivado synthesis automatically specifies a global buffer (BUFG) for all clock structures up to the maximum allowed in an architecture (unless otherwise specified or controlled by the synthesis tool). As discussed above, the BUFG provides a well-controlled, low-skew network suitable for most clocking needs. Nothing additional is required unless your design clocking exceeds the number or capabilities of BUFGs in the part.
Applying additional control of the clocking structure, however, may prove to show better characteristics in terms of jitter, skew, placement, power, performance, or other characteristics.