There are multiple scenarios in which an object can become impacted/invalidated based on the changes done to the existing code for any of the objects.
If you are using deployment groups, the validation will be done with in the steps.
If you have automated the deployment using the BAT Scripts or Shell scripts then you can use the ‘validate’ command at the end of the script to run the validation for all the objects.
If you need to validate the complete folder then you can do it using the below steps in the Repository Manager.
The other option is the wizard which pops up when you do the copy paste of the folders using the Edit menu. At the end of the wizard, you will have the option to select the validation option.