■ V-た ままです
Meaning: “Remain in [a state] / [something] was left in [a state].”
V-た まま is used to describe that the state resulting from an action remains unchanged.
Example: 電気[でんき]が ついた ままでした (The lights were left on).
そのまま means “without changing the state,” and is often used when doing the next action while in the same state.
For example: そのまま 食[た]べる (to eat without cooking or seasoning).
This structure can also describe a situation where the speaker notices that something has been left in a particular state,
e.g ドアが 開[あ]いた ままです (The door is left open).
■ V-るのに いいです
Meaning: “Good for [verb-ing] / Useful for [verb-ing].”
Example: ごみを 減[へ]らすのに いいです (Good for reducing waste).
This expression is used to explain that something is suitable or beneficial for a particular purpose.
に いいです to express that something is good or useful for a purpose. And also this can be used with both verbs and nouns.
For example, 環境[かんきょう]に いい (good for the environment).
It can also be used with verbs like 使[つか]います (be used for) and 役立[やくだ]ちます (be useful for) in similar contexts.