Advantages - This often reduces cost of ownership by allowing for large bulk purchase agreements with vendors as well as standardized training. Standards can also be guidelines created by government, industry, or other organizations that have been formally adopted by the organization as an organizational standard.
Standards are essential so that a common baseline can be established and implemented. Having a common basis for the overall organization is better than having each individual department operating under its own separate (and in some cases non-compliant) environment. This helps reduce the seams that can develop between sections, departments, and subordinate organizations.
Disadvantages -
A vulnerability in the selected product can place the entire organization at risk. There is also the risk of a vendor not supporting the product, or it becoming too expensive to maintain/license.