Also never forget that all of this is covered in detail in Help > Jaws Help Topics. In this case here is what is said about speech on demand:

Speech On Demand

Speech On Demand is a feature that allows you to limit the amount of JAWS speech you hear as you navigate windows and documents or perform other actions using hot keys. By default, when using Speech On Demand, JAWS only announces actions that are associated with a limited set of hot keys. In addition, mouse echo and typing echo are still available, which allows JAWS to read text that you point to with the mouse pointer and speak characters and words as you type. You can quickly toggle between Speech On Demand and full speech using a convenient layered command, or even make Speech On Demand the default speech mode when JAWS starts.

For JAWS users who rely heavily on Braille or for users of Fusion that can see well enough to use the screen for tracking focus, too much speech can be overwhelming while navigating using the keyboard and mouse. However, users still want to be able to use speech to read once they have moved to a location on the screen, or just checking a Window Title, column heading in a table or spread sheet, or even reading the time from the System tray. In both these situations, Speech On Demand can be very helpful. You will find that switching applications with ALT+TAB or using ARROW keys to move through a document are silenced. Speech is only triggered when using a limited set of reading commands such as speaking the current character, word, line, paragraph, or doing a Say All. You also have the option to completely turn off speech.

Layered commands to toggle Speech On Demand or Mute Speech:

• Press INSERT+SPACEBAR followed by S to toggle the speech mode between Full Speech and either Speech On Demand (the default) or Mute Speech.
• Press INSERT+SPACEBAR followed by SHIFT+S while Full Speech is disabled to toggle between Speech On Demand and Mute Speech.

By default, JAWS always returns to Full Speech when restarted after these keystrokes have been used. To make permanent changes to the default settings, do the following:

1. Press INSERT+F2, and select Settings Center.
2. If you want changes to only apply to a particular application, select it from the Application list. Otherwise, press CTRL+SHIFT+D to load the default settings file.
3. In the tree view, expand the Speech Options group.
4. Press the SPACEBAR on Speech Mode to change the default choice between Less Speech or Full Speech. Full Speech is selected by default.
5. Press the SPACEBAR on Less Speech Options to change the default choice between Mute Speech or Speech On Demand. Speech On Demand is selected by default.
6. Expand the Speech On Demand Options group.
7. If you do not want any reading hot keys to speak with Speech On Demand active, use the SPACEBAR to clear the Allow Reading Commands check box. Reading commands are spoken by default.
8. If JAWS Mouse Echo is enabled and you want to hear text as you move the mouse with Speech On Demand active, use the SPACEBAR to select the Allow Mouse Echo checkbox. This checkbox is cleared by default.
9. If JAWS Typing Echo is set to Characters, Words, or Characters and Words and you want to hear what you are typing with Speech On Demand active, use the SPACEBAR to select the Allow Typing Echo check box. This checkbox is cleared by default.
10. Choose OK to save your changes and close Settings Center.

Note: When set to Speech On Demand or Mute Speech, all sounds played by JAWS are also muted. This includes the sound heard when pressing INSERT+SPACEBAR to enter Layered Keys mode as well as the sound heard when completing an address in Outlook.

Designated Reading Commands

The tables below list the preset designated reading commands for Speech On Demand. These include commands available in all applications as well as commands specific to Word, Excel, and Outlook.