Question

Why is simple interest useful for planning parts of your financial future?

Answer 1

I believe the answer is: Simple interest is very regular and can be calculated in advance.

This mean that the amount of simple interest would not be affected by the performance in the market, which make it become very predictable and can be calculated in advance so you can make necessary adjustment in your expenditure without compromising your saving.

Answer 2

Simple interest is very useful for planning parts of your future plan because it  simply helps you to accurately calculated the costs of of you actual financial plan. In time the interests increases the longer the time passes by, that's why even if it's a simple interest, it gives a big impact.