Its useful in a sense that you dont need to use the exact keywords to rank for them sometimes and a single page can rank for thousands of different keywords all related to each other.
As far as LSI tools go, feel free to use them for research purposes but Google has confirm that they in fact dont use LSI but im sure they have a similar more sophisticates algorithm plus access to billions of queries to how the users interact with them to make this connections.
LSI will play an even bigger role but has been around for some time now. Essentially all LSI “keywords” are is Google’s way to naturally see if a website has been built to cover a topic authoritatively vs a website simply putting out content to satisfy Keyword searches. Remember it is all about providing a user the best result possible and the Google “Bert” update brings that to the next level. With natural language understanding, it is easier for the AI to truly identify if the website as a whole will cover a topic with authority when answering Queries in search.