As the title, it will store in the place as same as the last open file stored.
I don’t think this is a right choice, I tend to store the new file in the new folder I created.
Unless you explicitly create a file inside of a folder either from your operating system or by right-clicking the folder in Obsidian and selecting New note, then Obsidian will save the new note according to your settings.
There are also plugins that can effect where new notes are saved: Daily notes, Zettlekasten.
Daily note and Zettlekasten is the special one. Create a new folder and then create a common file, it won’t store in the new folder, right now it store in the last open file’s folder