Note if you are logged on to your Google account (like gmail) ALL your Google searches going back years are kept and can be viewed by you if you want to.
I went and looked at my Google search history and found things I had searched for years ago.
If you would rather these search details were deleted you can do it as follows:
https://support.google.com/websearch/answer/465?hl=en
Being able to access your search history going back years could cause problems if a husband/wife (or boyfriend/girlfriend) wanted to check up on their partner.
If the husband (for example) left his computer logged on his wife could look at all his searches going back years.
So if a person suspects their partner is up to no good (searching for dating sites etc) then it could cause problems in the relationship.
Best to delete all your history now.