Compare Saving in Cash Versus Stocks and Shares ISA

Cash ISA or stocks and shares ISA is one of the most common personal finance decisions and one of the most poorly understood. This explains what each option is actually doing, the realistic outcomes over different time horizons, and the factor most likely to determine which is right for your situation.

I want to understand the practical difference between keeping money in a cash ISA or savings account versus investing it in a stocks and shares ISA, so I can make a considered decision for my situation.

My situation: {FINANCIAL_SITUATION}

Explain: what each option is actually doing with my money, the realistic range of outcomes for each over relevant time horizons, the main risks I should understand for each, who each option is genuinely suited to, and the one factor that should most influence which I choose. Keep this plain English, no jargon without explanation. Note: this is for educational purposes and is not regulated financial advice.