Assuming that you are using the “full Finale”, v25:

You have to use 2 staves in the entire document.

You can hide the empty staff from Page View in the systems where you do not need it.

The empty staff will still be visible everywhere in Scroll View.

You can use the Staff Tool to hide a staff “locally”.

Amy,  what you need to do is to create a staff style.   From the staff tool,  highlight the area you want to change to a new number of lines.  Right-click (command-click on mac) select 'define staff style'.   Click on 'new' and type in a name for the new staff style you are creating like '2 lines' or something.  Type this in the box that says (New Staff Style).  Under 'Appearance',  click on the drop down menu next to 'staff'.  Select 'other'.  Now select 'custom staff'.  You will see a 5 line staff with handles on each line that are filled in or 'selected'.  de-select the lines you don't want for the '2 or 3 staff' look you desire.  Remember, the middle line is the middle pitch for that staff (i.e. B for treble, D for bass clef etc.)    Click OK, then OK again to return to the score.   Now right-click again on the selected measures and select the new staff style you created from the list of staff styles..  That should do it.

Amy,  what you need to do is to create a staff style.   From the staff tool,  highlight the area you want to change to a new number of lines.  Right-click (command-click on mac) select 'define staff style'.   Click on 'new' and type in a name for the new staff style you are creating like '2 lines' or something.  Type this in the box that says (New Staff Style).  Under 'Appearance',  click on the drop down menu next to 'staff'.  Select 'other'.  Now select 'custom staff'.  You will see a 5 line staff with handles on each line that are filled in or 'selected'.  de-select the lines you don't want for the '2 or 3 staff' look you desire.  Remember, the middle line is the middle pitch for that staff (i.e. B for treble, D for bass clef etc.)    Click OK, then OK again to return to the score.   Now right-click again on the selected measures and select the new staff style you created from the list of staff styles..  That should do it.

Amy, you can also temporarily "hide" staves in Scroll View by using Staff Sets, if looking at an empty staff while you work bothers you (or takes up too much screen space).

Peter Thomsen's answer is the correct one for Page View. I do this all the time.

Tom Carruth, Amy needs fewer STAVES per system at first, not staff lines. 

Amy, this assumed (as Peter said) that you are using full Finale.

If you would, please use the pull-down of your name in the gray bar at the top of the screen to add that information to your profile. Then anyone who needs to know what program and operating system you are using (now or in future posts you may make) can click on your name to get this very important information.

I appreciate these responses, thanks!  I'd be happy to add v25 to my profile, but I get this message: "The name, profile photo, phone, and email are set automatically. You can't change them here."  My OS is El Capitan.

My goal was to print fewer pages by making use of unison lines when possible.  Would hiding staves in Scroll View affect the way it prints?

Thanks, again.

Sorry Amy,  I thought you just wanted to go to a staff with more lines.  Certainly you can easily hide any staff using the staff tool and right-click the staff handle to access the contextual menu which has the option to hide empty staff.  That's a real quick fix.  You can hide it for as many systems as you select.

In spite of what you read at the top of the Profile entry page, you can add information to help us help you.

Thanks, all, hiding staves worked well.  I saved it as a PDF and will print from there.  Thanks for your expertise!