It's called roleplay. While I find myself in this position as well sometimes. a) most of the time it's pretty obvious what advances a conversation. b) always say what you WANT to say. Sometimes it might me more text/info sometimes advancement, but you do not "loose" anything except maybe a few minor backgroundinfos you do not need anyway.
It's almost never obvious, plenty of times you'll have like 3-4 options with questions, one question will advance the dialogue and the others will give you more info.
Also this has absolutely nothing to do with "roleplaying," if I were roleplaying I'd be able to ask all info before advancing the conversation because that's how I'd want to do it.
I want the background details because I like having that info, it helps build up the quests/characters/world when you have more background information, and missing out on it because you select a vague response that may or may not advance the dialogue isn't enjoyable for people that'd like to expand on as much dialogue as possible.
Mass Effect does this by color coding their dialogue choices so it's clear when you're choosing an option that will simply give you more info and others which will advance the conversation forward.
Doing this in no way takes "away" from roleplaying or anything, it merely lets you make more informed choices.