Having accounts in too many exchanges is not a good practice because of security issues. Creating an account in multiple exchanges is tedious and remembering all the passwords is also difficult.

Storing the cryptos in the exchanges is also not safe due to hack issues. It is better to choose the best exchange for trading instead of trading on different exchanges.

I trade on an exchange that is an aggregator exchange(Coinswitch) of many exchanges. Here we need not have to create an account and we can trade at the best rate by comparing the prices at different exchanges and trade at one place.