There are 2 scenarios where we need the Webpart Maintanance Page to delete trouble making webparts from the current page:
a. At times the webpart we are developing might have code errors due to which the whole page hangs up or stops working entirely and redirects you to a SharePoint error message stack trace page.
b. Most of the times, we just tend to "Close" the unused webparts, while we are setting up our pages. But the webpart still remains hidden on the page and loads each time the page is called, even though not in use.
This might result in performance bottle necks, while loading the page as it loads unused webparts as well. The quickest and shortest route to fix the above is switching to the Page's Web Part Maintance Mode.
So, for eg: if your SharePoint Landing Page URL looks like this: http://sharepointfix:9999/Pages/default.aspx
In order to quickly switch to this pages webpart maintanance mode, you need to append the above URL with a ?Contents=1 query string parameter like this:
You can then delete the unused/not required webparts from this page, by checking on the webpart and clicking on the Delete option:
I hope this helps.