Quick take
Do not buy RO automatically for plants. Start with the actual problem: carbon can help chlorine/chloramine, while RO is more relevant when dissolved salts or very hard water are causing trouble.
Chlorine and chloramine
Carbon filtration can reduce disinfectants without stripping nearly all minerals from the water.
Hardness and salt buildup
Very hard or mineral-rich water can leave deposits in pots and soil over time. RO can reduce that dissolved load.
Sensitive plants
Some species react more strongly to salts or fluoride, but the right solution depends on the plant and local water chemistry.