A benefit that hasn’t been mentioned yet, as far as I can see, is that being able to speak more than one language, especially in bilinguals, sets off the beginning of dementia by up to five years. Lucky me!
As for the other benefits, for me as somebody who works as a tour guide with six highly requested languages (English, French, German, Italian, Russian, Spanish) + a seventh that is a minority language (Catalan), it means (setting the Corona virus pandemy aside) that I get more requests than people who speak just one or two foreign languages. It means I’m also more flexible: e. g. in my city we’ve got lots of tourists from cruise ships, so if there are few bookings for tours in one language, they may be more bookings for tours in another language. On one occasion, due to various circumstances, the tour operator’s request for me changed back and forth between four (!) of my working languages, but not working on that date was never an option.
News coverage: e. g. in the Spanish-Catalan conflict about Catalonia’s independence movement, the news coverage in the German newspapers is largely and uncritically pro-Madrid. Since I am fluent in both Spanish and Catalan, I am able to research and process information in both languages, which means I am less biased in favour of the central governments handling of the crisis during last years. It may, however, mean that I am more biased in favour of the independence movement (though not necessarily pro-Generalitat).
It may also be that a certain topic is well covered by the media of one or two countries with different languages, but not by the media in other languages, e. g. the Mistral affair between France and Russia received only one or two short articles in German , but was extensively covered over several months in both French and German media.
Information research: I am able to use scientific literature in various languages without having to wait for the translation into English or German.
Literature: the advantages are largely the same as with news coverage and information research. I do not depend on translation, plus I get to savour the flavour of the original language. Sometimes I may compare translations (and find out that in “Les Trois musquetaires” Dumas uses two or three dates for a short hand-written note, while this is corrected in the Russian translation), but usually I prefer not to read translations, since I am very well aware what may become lost in translation, also working a translator myself.
I’d also like to confirm virtually everything that Evan Wynn has written in his answer.
The only thing I cannot confirm is that learning a language is humbling. I’m frequently complemented on my skills in various languages, but to me it has always come easy and naturally. So even if I can intellectually understand why people are in awe, I cannot really understand it emotionally - unless I compare it with other areas in which I struggle to achieve anything that could be called proficiency.
