I think voice chat is EXTREMELY helpful when doing any 8 man content, especially if it has annoying mechanics or mechanics that do require more than one person coordinating. Like Ramuh EX. (god hate that fight) I do think though it is possible for a group or a static to not have a voice chat, however it would require people to know fights and be able to react to situations. I do love the convenience of having people being able to quickly saying they need something. "I need heals" "Oh I'll raise" "move here. now move there" it's awesome. It's definitely something players should look into, however it is not needed but you do need to make sure to put in the effort for the content that you are trying.