Unmanaged packages should not be used to migrate components from a sandbox to production organization. Instead, use Change Sets.
Having unmanaged package installation approach in production, you can't Uninstall the package if it is being referenced by component which is not part of that package
You can not upgrade unmanaged packages. You will have to uninstall the previous one.
You cannot overwrite a component which has the same API name in production but not part of the package and package also contains the component with same API name.
In production, you don't have enough development controls to resolve the dependencies issues. If package starts causing issues, you will be stuck due to lack of controls.
With changesets, above issues don't occur. Also, you can build a single unit of changeset and upgrade it by cloning and adding components.
Unmanaged packages should not be used to migrate components from a sandbox to production organization. Instead, use Change Sets.
Having unmanaged package installation approach in production, you can't
Uninstall the package if it is being referenced by component which is not part of that package
You can not upgrade unmanaged packages. You will have to uninstall the previous one.
You cannot overwrite a component which has the same API name in production but not part of the package and package also contains the component with same API name.
In production, you don't have enough development controls to resolve the dependencies issues. If package starts causing issues, you will be stuck due to lack of controls.
With changesets, above issues don't occur. Also, you can build a single unit of changeset and upgrade it by cloning and adding components.
Please refer below links to know more.
http://salesforce.stackexchange.com/questions/88331/why-not-use-unmanaged-packages-to-migrate-metadata-to-production
https://help.salesforce.com/articleView?id=sharing_apps.htm&language=en_US&type=0
https://developer.salesforce.com/docs/atlas.en-us.appExchangeInstallGuide.meta/appExchangeInstallGuide/appexchange_install_installation.htm
Hope this helps you!
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Sandhya