Constraints are an important component in SQL Server and act to maintain integrity in the database by putting rules in the data inputted. These include the Check and Default constraints that play the role of data validating and normalization.

Check Constraint 

The Check constraint is one of the amazing features of SQL Server which helps to validate what may be entered into the individual column. They execute or impose certain restrictions in the form of a condition or multiple conditions on the data, which is either made to be entered into a table or modified in a table. When the Check constraint is used, the SQL Server decides whether the condition put in the constraint is fulfilled or not for every record. 

For instance, the following Check constraint can be created: The salary column only contains values more than zero. It does not allow any entry that is not valid, which enhances the quality of the data entered by the business since the data entered will conform to the business rules a business requires. 

The check constraints are widely used to validate the data consistently at the time of entry so that working with wrong data is avoided. However, we should properly devise these constraints because intricate checks have repercussions on the boundaries of big or dynamically evolving tables​. 

Default Constraint 

Default constraints in SQL Server enable a column to be given a standard value which is imposed automatically when no value is entered. This makes certain kinds of columns always contain valid and expected values that the system or a programmer will always be sure of even if the user omits the particular value. 

For instance, you can specify the Default constraint on a “status” column to make the default value of newly created rows active. This is especially helpful because some columns should contain the same value unless explicitly defined by the user. 

Some of the default constraints like Check constraints; work to ensure a table’s accuracy by reducing incidents of null or missing values. 

Importance of Using Constraints 

Check and Default constraints are useful in that they assist in the protection of your database’s data integrity. These provide a way to avoid entering wrong or partial data within a database since we store accurate and genuine information. : Besides, they free applications from many checks or application-side validations that can be performed at the database level, thus increasing database stability and decreasing the number of possible errors. 

• Check Constraints: Verifies data as they are being input or altered to conform to established patterns on data format (e.g., age>18). 
• Default Constraints: This one assigns a particular value to a column in case the specific data were not entered. 

With such constraints implemented, you guarantee that your data maintained in the database is consistent with your business rules and as well maintaining data integrity in the long run. 

Conclusion 

To sum up, it can be stated that both Check and Default constraints are very useful in SQL Server for preserving the data integrity and business rules. Applying these constraints correctly makes it possible to accept only good data necessary for a database thus cutting costs of having to rectify other data which could be inaccurate. Such constraints are very important in designing and managing databases and SQL Server offers great ways of implementing these constraints.