Google has long favoured results which include all your search terms, which means that using a plus sign doesn’t always make a huge difference, but it is still handy in contexts where Google assumes you meant something else or automatically expands abbreviations. However, as Google Operating System points out, the plus sign is now being ignored. If you want to force Google to search for a specific term, you have to put it inside quotation marks. It’s not a major nuisance, but it will require old hands to adjust their tactics. Fortunately, the minus sign to exclude specific terms or sites remains active.
Google’s Plus Operator, No Longer Available [Google Operating System]