In Voyant the term plans = scenarios (including the base plan). A client file contains one or more plans, always beginning with a base plan.
On the Preferences screen, the Plan Preferences -- the list of panels to the right side of the screen -- are applied to the individual plans within the client case you are presently viewing. If you want to change a preference in the plan you are viewing, you would make this change in the panels in Plan Preferences, to the right side of the screen, and click Apply, bottom-right.
The System Preferences, to the left side of the screen, are used by the software only going forward, as the initial set of preferences when you create entirely new client cases.
Altering system preferences will never affect the settings in any of the client cases you have already created. Once a client case is created, the Plan Preferences are used in that case from then on.
The default Mortality Age offers a good example of how System Preferences work. You may have the default mortality age set to 90, initially, in your software's System Preferences. If you create a new client case for John Smith, John's mortality age will be set at 90. If you change the default Mortality Age in System Preferences to age 100, John's mortality will remain at age 90. However, if you were to create a new client case for William Bradley, William's mortality age would be set at age 100.
System Preferences are usually saved only locally for your user account, on the computer you use to access the software. If you install Voyant on another computer, you will probably need to set the System Preferences on that computer, if you've been customising them. There is an exception to this rule. Firms that subscribe to the Voyant rebranding (white labelling) service do have the option to add the firm's preferred set of system preferences included in their semi-bespoke version of Voyant Adviser. This service allows for updates to assumptions to be easily distributed to all of the advisers and paraplanners within the firm.
Plan Preferences are plan specific. Unlike System Preferences, they are integral to the client case and will follow the client case wherever it goes. So if a colleague opens your client case for John Smith, she or he will see the case bearing the set of preferences that you selected for it.