Good question! Like Miyu-san said, I unconsciously use "から" too. So I run a little search to explain it logically. I hope this helps you understand it. Usually から is used to show a cause or reason like this: 雨が降ったから、道路がぬれています。(cause) 昨日は体調が悪かったから、早めに寝た。(reason) から also has a little different meaning. With から, you can show a premise or precondition to ask for some actions such as a request or an order. 車で送るから、一緒にパーティに行ってくれませんか。 I'm going to give you a ride. So, would you go to a party with me? 絶対幸せにするから、結婚してください。 I am sure that I will make you happy. So, please marry me! から ending sentence is a short version of it, implying a hidden request. 早く戻るから。（待っていてね。） I'll be back soon. (please wait for me.) 冷蔵庫にご飯が入っているから。（温めて食べてね。） I put meal in a fridge. (please warm and eat it) I hope this is helpful!

「ここが君のクラスだから（おぼえておいてね）」 「咲でいいから（そうよんでね）」 In my opinion, we omit the last phrase. Because we know what you want to say. Those are the same meanings as 「ここが君のクラスです」「咲でいいよ」 To be honest, we use から unconsciously in this case. I think there is not difference of nuance between から and no から. Besides these, we offen use 食べてていいから. Same as 食べてていいよ. This is interesting and difficult question for me. I never thought about that. I will be happy if I can be of any help.

Got it! However, there are a lot of things regarding Japanese that for us are difficult to understand at first; sentence-final particles are a good example of the differences in conveying a message between Japanese and English.

Insteresting question! I often use から this way whitout knowing any rule... I just feel it sounds more natural in some cases and Japanese people use like this a lot.