But I like saving bitcoin and several altcoin assets on exchange market, easy for selling when price suddenly pump witjout have to move exchange account when trading.
This is convenient if you are an active trader, but there are definitely additional risks that can be avoided. Even if we are talking about an amount that is not a pity to lose, it can still be a loss of funds, which we do not need. You won't spend much time moving coins from wallet to exchange if needed, but it can save you money.
Storing bitcoin on an exchange site would really be convenient if you are an active trader however the risk could provide you significant hassle in the long run. For security purposes, bitcoin wallets such as bitcoin core, electrum would be much better as it will be harder to hack. Unlike with exchange sites which you can easily encounter notification on a daily basis of someone trying to log in with your account. (Based from experience from various exchange sites especially famous ones).
Also, it is common for exchange sites to conduct maintenance and you won't be able to withdraw your funds on your account. So yes, there are most risk and inconvenience that can be encountered from exchange sites to software wallets.
As with the OP's question, I guess having multiple wallets would be good if you have a significant amount of bitcoin (does not mean it must a high amount). I mean, if you an insignificant amount of bitcoin, you will need to shoulder the multiple transaction fees that would cause you losing funds with bitcoins.
For me, I have atleast 3 kinds of wallets where I store my bitcoin. I have local wallets for convenience, in case that I will require emergency funds or fiats to dispose with. A software wallet for saving my coins and for crypto transaction. Lastly, I store some coins including other crypto on exchange site to do some trading from time to time. However, I guess it would be better to have a physical hardware wallet instead for better security on your coins.