If it's planned to run a VM a year or 3 years with the same size or same VM series it is good practice to do this with Reserved Instances.
Some more information here:
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/understand-vm-reservation-charges
https://learn.microsoft.com/en-us/azure/virtual-machines/reserved-vm-instance-size-flexibility
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Regards
Andreas Baumgarten