Software as a Service (SaaS) is a model of software distribution in which software is hosted at one place and is made available on subscription basis over the internet.
The biggest advantage is user of software does not need to install application in his premise. So cost for server/hardware, its license, maintenance and support is reduced to zero. Customer just needs a web browser to use software.
The second biggest advantage is software service can be used from any location since it is available over internet.
SaaS offers better payment option in terms of subscription that can be monthly or annually. So instead of a huge upfront license fee, it lessens financial burden. Also customer can terminate SaaS and stop these recurring charges.
Scalability is one more advantage of SaaS model. Customer doesn't have to worry today about future needs of expanded hardware/software needs. Customer has option to use scalable service as per the current business need and option to expand or reduce usage in future.
Customer does not have to be stuck in one version of software service. SaaS provider will ensure automatic updates in software. So no IT team required at customer's end to do this or any other maintenance job.
Customer is heavily dependent on SaaS provider for application's up time, security, changes in service or disruption. So a professional SaaS provider should be contracted who has clear service level agreement (SLA) terms.