* Seamlessness - it has an in-built processing pipeline (using queues, service bus etc.), whereas with Lambda you'll have to do a little more work to connect the components e.g. S3, SNS.
* Scalability (although both AWS and Azure offer auto-scaling) - Lambda has an execution timeout of 60 seconds for functions. If the functions are I/O bound then WebJobs is more suitable, else Azure Batch offers better CPU bound work support.
* Ease of deployment - 'drop and use', which I don't think Lambda offers out-of-the-box because there seems to be dependency on Node.js?! The WebJobs dashboard under Azure Portal is a great way to track invocations and logs.
* Cost - WebJobs comes free with App Services (Web Apps)
The one and only shortcoming of WebJobs seems be the lack of recurring tasks (but there's a workaround by adding the job back to the queue on its completion).
Further reading:
http://www.troyhunt.com/2015/01/azure-webjobs-are-awesome-an...
http://www.troyhunt.com/2015/04/orchestrating-massive-parall...
http://www.hanselman.com/blog/IntroducingWindowsAzureWebJobs...
An on-premise alternative can be Hangfire, Sidekiq or Quartz.