It’s not bad for your brain, but it doesn’t continually build your brain. Most people who do it (like anything else) eventually reach a comfortable plateau and don’t push themselves beyond it.
Most non-competitive intellectual pursuits are like this. Activities where you are either competing against someone or being judged by someone tend to be better for continually challenging your brain, because there’s more of a motivation to keep upping your game. Something with no competition and no audience like a crossword puzzle tends to stagnate pretty quickly.← Frequently Asked Questions