SharePoint - event handlers

The main differences between SharePoint event handlers and SharePoint workflows are:

Initiation
SharePoint event handlers are automatically initiated, while SharePoint workflows can be initiated either automatically or manually.

Response
A SharePoint event handler always responds to an event that has taken or is taking place on an item, while a SharePoint workflow does not necessarily have to react to an event that is taking place. While it can react to an item being created or changed, you can also manually start a workflow after an item has been created.

User Interaction
SharePoint event handlers have no user interface, so users cannot interact with event handlers. On the other hand, you can create either ASP.NET or InfoPath forms to provide user interactivity with SharePoint workflows. And you can add even more interactivity by using SharePoint Tasks lists along with the workflow.

Duration
SharePoint event handlers run for a short period of time (generally seconds), while SharePoint workflows may run for a much longer time period (days, months, or even years).

Robustness
Since SharePoint workflows are hydrated and dehydrated, they can “survive” server reboots, while SharePoint event handlers cannot.

SharePoint event handlers vs. SharePoint workflows

The main differences between SharePoint event handlers and SharePoint workflows are:

Initiation
SharePoint event handlers are automatically initiated, while SharePoint workflows can be initiated either automatically or manually.

Response
A SharePoint event handler always responds to an event that has taken or is taking place on an item, while a SharePoint workflow does not necessarily have to react to an event that is taking place. While it can react to an item being created or changed, you can also manually start a workflow after an item has been created.

User Interaction
SharePoint event handlers have no user interface, so users cannot interact with event handlers. On the other hand, you can create either ASP.NET or InfoPath forms to provide user interactivity with SharePoint workflows. And you can add even more interactivity by using SharePoint Tasks lists along with the workflow.

Duration
SharePoint event handlers run for a short period of time (generally seconds), while SharePoint workflows may run for a much longer time period (days, months, or even years).

Robustness
Since SharePoint workflows are hydrated and dehydrated, they can “survive” server reboots, while SharePoint event handlers cannot.