I would like to ask a question about the sentence ending particle よ and when it is okay not to use a sentence ending particle in informal japanese. I know that よ is used when the listener asks you something and you answer or when you want to correct the listener's opinion but would it be okay to use in other situations? For example, if you want to tell your friend that you went to tokyo yesterday without your friend asking what you did the day before, is it better to say「そういえば、昨日、東京に行った」or 「そういえば、昨日、東京に行ったよ」? Please tell me if there are better options. Thanks in advance!
I think as a general rule you don't often want to use よ when answering a question unless you think your answer will surprise the person asking the question.
However, in your example about Tokyo, you are not asking a direct question, so I think it's better to use よ when you speak about the (surprising) thing you did. Removing よ from that sounds oddly neutral to me.
よ can drastically change the meaning of certain things. For example, if someone asks if you for something you can use "いいよ" to agree in the sense of "sure!". However, saying simply "いい" (or ”けっこう") can actually mean "no thanks". Of course each of these has a certain tone of voice that goes along with them.
Besides the function you mentioned, it can also prompt the listener to take somewhat proper action. In this context, it can imply that you want him/her to listen to consequence of the story. In that sense, you can naturally use it.
Like in your example,
This よ sounds very natural because
- You're talking to a friend. (where よ is very unlikely to be impolite)
- You're introducing new information into the conversation.
It's using よ when talking to people you don't know, or anyone socially above you could easily be considered presumptive and impolite. (best to avoid よ with your boss or teacher)