What are the positives and negatives of using the multi-currency function on quickbooks?

I use quickbooks online for the company I work for, and when we started using it our accountant at the time advised against turning on the multi-currency function. I am not sure why he advised against it. Currently, we just convert the money ourselves and enter it all as US Dollars.

Now, I am considering linking a Euro banking account, and I am faced with this question again. I am assuming I have to put on the multi-currency for it to work, I hope it will work.

Last time I looked into it (years ago) there was a warning that once you turn it on you cannot turn it off.