Difference between DoSave and DoSaveNow?

Syntax
DoSave()
Description
Use the DoSave function to save the current page. DoSave defers processing to the end of the current PeopleCode program event, as distinct from DoSaveNow, which causes save processing (including SaveEdit, SavePreChange, SavePostChange, and Workflow PeopleCode) to be executed immediately.
DoSave can be used only in FieldEdit, FieldChange, or MenuItemSelected PeopleCode.

DoSaveNow

Syntax
DoSaveNow()
Description
The DoSaveNow function is designed primarily for use with remote calls. It enables a PeopleCode program to save page data to the database before running a remote process (most frequently a COBOL process) that will access the database directly. It is generally necessary to call DoSaveNow before calling the RemoteCall function.
DoSaveNow causes the current page to be saved immediately. Save processing (including SaveEdit, SavePreChange, SavePostChange, and Workflow PeopleCode) is executed before continuing execution of the program where DoSaveNow is called. DoSaveNow differs from the DoSave function in that DoSave defers saving the component until after any running PeopleCode is completed.
DoSaveNow can only be called from a FieldEdit or FieldChange event.

If you call DoSaveNow and there are no changes to save, save processing is skipped entirely. You can call SetComponentChanged right before you call DoSaveNow. The SetComponentChanged function makes the Component Processor think there are changes and so will force full save processing.