Switching to another Google site usually disregards your search
Now that the black navbar is gone for good and that the app launcher will be the primary way of navigation through the various Google products, you might as well get used to the new layout. The switch to the app launcher has a few advantages, perhaps, for one it saves up a bit of space by getting rid of the navbar.However, there are plenty of annoyances. The biggest, of course, is that you have to click two times to get anywhere, three times if the product you're looking for is not among the nine Google depicts in the main page of the app launcher.
But the most annoying change, to some users at least, is the loss of the search term when switching sites. Previously, if you searched for something on the main Google page and then switched to another Google site, like YouTube, from the navbar, the search term was maintained.
This did not work for all products, but worked for many. Of course, at the same time, the search term was maintained when switching from the generic "web" search to "images" or "videos" via the search tabs. This still works now.
With the app launcher though, selecting YouTube will just send you to the YouTube homepage, your search will be lost. This is very annoying to the people that started a video search on Google rather than on YouTube. You could argue that this is what the "video" search option is for, but most people only want to look through YouTube videos.
Thankfully, there is some hope. The search term is sometimes kept even if you use the app launcher. This only works when you start a search from the omnibox or the search box. For example, if you search for for "Paris" through your browser and then select YouTube from the app launcher, you'll get a list of video results for "Paris."
But if you type your query into the search box on the site, this won't work. Obviously, the feature needs more work, but it is at least indicating that Google wants to keep this functionality and that it may be built back into the site at some point.