The Apache License, v2.0

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2. Grant of Copyright License

Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense and distribute the Work and such Derivative Works in Source or Object form.

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3. Grant of Patent License

Subject to the terms and conditions of this License, each Contributor hereby grants to you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including cross-claim or counterclaim in lawsuit) alleging that the Work or a Contribution incorporated within theWork constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.

While the meaning of the Copyright License provision is rather clear, I did not get the meaning of the Patent License provision.

• Which advantages does the "Grant of Patent License" provision further give to Contributors? Why are they useful?
• Is the "Grant of Patent License" provision useful only in case of patent litigation?