Posting an answer as it's all going on in comments and should be an answer instead.
Hovering isn't as user-friendly as you'd think it is, we asssume it's a good option but it comes with many negatives, namely:
- flashes of opening/closing items when hovering over them by mistake
- hovering and then moving the mouse out the way closes it when that might not be required.
- If you add a delay to counteract this issue that means when the mouse is out of the area it's covering up some content on the main page - and you probably want to see the content instead of the menu at that point.
- Hovering requires more precision to interact with than a click does as it requires the user move their mouse there, keep it in one place and then move the mouse down to the option they want, all the while keeping it within the small boundry area of the item to stop it closing on them.
- Hovering doesn't work on touch devices - I know there are workarounds for this - allowing click to open for some devices and hover for others - but that needs user agent detection, or CSS variations and it's still not guaranteed to trap all devices (as I found from experience).
- You have to determine the optimal delay time between hovering and displaying - just enough so that users don't start clicking it thinking nothing is happening but no so fast that it starts flashing around when rolling over it.
Most of the issues are going to be around adding in the correct delay period, but this delay period is going to be percieved differently for different users.
Also, they might start clicking it instead of hovering; so what do you do in this situation - they've hovered, then think they need to click so they do so, but then menu has since opened due to the hover delay period - now what? Do you close the menu?
- Clicking the menu item again closes it - that's going to annoy users who didn't notice that it had opened via hover and have clicked thinking it's going to open.
- Clicking the menu doesn't open it - that's going to annoy people who want to dismiss it as clicking to open/close is a pretty common pattern.
Mixing in hover and click together as different interaction methods for the same control is always going to throw up situations like this, so it's safer to pick one and stick with it than try to compromise and offer multiple ones to try to please everyone.
There's a discussion on UX.StackExchange about the benefits of hover menus if you (or anyone else) is interested. This is a slightly different case, but it's still useful anyway.
Are hover menus in headers easy to use?
Basically - introducing hover-interactions brings more problems than it solves.