Why?

Calculators are helpful, but if you use them too often, you might not be able to do calculations as simple as 38*25! Also, when doing Algebra, calculators are allowed, but most teachers don't allow calculators in calculus. Calculators aren't allowed in competition, either. So, it is best to practice without a calculator!

Calculators are bad for learning if you want to learn then don't use a calculator. They do the solving for you so you don't get used to solving those things. so it's not that good to use a calculator if you want to learn!