Today, I have come across different workflow related limits for SharePoint Server 2010.
Limit
Maximum value
Limit type
Notes
Workflow timer batch size
100
Threshold
The number of events that each run of the workflow timer job will pick up and deliver to workflows. It is configurable by using Windows PowerShell. To allow for additional events, you can run additional instances of the Microsoft SharePoint Foundation Workflow Timer Service.
Workflow postpone threshold
15
Threshold
15 is the maximum number of workflows allowed to be executing against a content database at the same time, excluding instances that are running in the timer service. When this threshold is reached, new requests to activate workflows will be queued to be run by the workflow timer service later. As non-timer execution is completed, new requests will count against this threshold. This is limit can be configured by using the Set-SPFarmConfig Windows PowerShell cmdlet. For more information, see Set-SPFarmConfig.
Note: This limit does not refer to the total number of workflow instances that can be in progress. Instead, it is the number of instances that are being processed. Increasing this limit increases the throughput of starting and completing workflow tasks but also increases load against the content database and system resources.