It is a metasearch engine, so you can tweak the sources of the results, default language, etc. I personally use all the default plus some more engines and all languages, then reduce results if I can’t find useful information. It has made searches easier for me, since you can find all types of information with just one click (Search | Images | Files | Academic | etc.) and multiple languages, but it can be not so welcoming to people that want simple searches.
I use Tab Stash if I’m about to close/restart the browser or I changed the focus of my research, but if I don’t wanna lose some keywords or something, I prefer to use KNotes (or any sticky notes) and write why some keywords are important and their context, so I don’t have to maintain too many open tabs. Just yesterday I had like 15 tabs and was overwhelmed lol