In the interests of SEO you’ll want to set good page titles, or h1 tags. Sometimes this will be a long title and the unfortunate thing about Magento is that it uses this same text for the menu item.
For example I want to set my category title to “Gorgeous Desktop Lamps”. That same text will be used as the menu text which is way too long, so you might want to just have “Desktop Lamps” for the menu.
Here’s a free plugin which will allow you to do that: