When you are creating or modifying sites or pages it could be very nice to see some reports. You can use the Site Usage reports but they give you reports on how many times your site has been viewed.
These are not the reports that I mean, I want to see some reports to know if there are some issues on my sites or pages. Again let SharePoint Designer be your friend and let him show you what is going wrong on your site.
Open a site and use the Site menu in the menu bar and navigate to Reports/Problems and pick an option:
In these screenshots I want to see if my links are OK but as you can see you have other options as well, for example what are the slow pages and do I have unlinked files.