As customers generally do not own the infrastructure or know all details about it, mainly they are accessing or renting, so they can consume resources as a service, and may be paying for what they do not need, instead of what they actually do need to use. Many cloud computing providers use the utility computing model which is analogous to how traditional public utilities like electricity are consumed, while others are billed on a subscription basis. By sharing consumable and ""intangible"" computing power between multiple ""tenants"", utilization rates can be improved (as servers are not left idle) which can reduce costs significantly while increasing the speed of application development.