the default settings are normally fine the way they are, but, being a personal thing, it'll all depend on your PC usage and what you are running CC for.
it can be customised to include extra areas, or exclude things you don't want touched for example.
the Pro settings are the same as the Free version as far as categories covered, so if you have been using CC for years, they will be no new learning curve.
if you do want to changing settings, you can tick the new option then Analyse to see what it does.
click the Cleaner button, top left column, all your selectable options for cleaning are there.
instead of clicking Run Cleaner (bottom right) you can click Analyse (bottom left) instead, that will tell you how your options will effect the cleaning process with any changes being done.
or you can right click each option and choose Analyse for that option.
Most people just run with the default especially those who aren't really into the technical side of things.
Unless you are comfortable around computers and understand what they do and how they do it, it is probably wise to leave things at the default setting.
It does no harm though Keith to do a bit of reading, so here is the link to the online documentation