Why so many items in content with no Spaceid?

[gaven]

We are working on the early stages of a cloud migration and in an attempt to make sense of the data we are looking through the database. 

In the process of trying to find the last revision of the home pages for the spaces in our Confluence I did a search for pages. After that search were I then added space names based on spaceid the numbers did not match. So I did the search below.

select count (*) from content where spaceid is null;
count
---------
2189193
(1 row)

When I look at the data for pages where spaceid is null I can find pages that line up with edits of pages in Confluence. I though it was for the drafts it appears not. 

So why are there so many pages with no spaceid in the database? Can I remove them or will that cause issues? 

We are using PSQL and I found this page https://support.atlassian.com/confluence/kb/removing-orphaned-draft/