Another thing is that people sometimes will get mixed up with exchanges versus holding their own bitcoin, so if you keep your coins on exchanges, there are some risks with that, yet personally, I am o.k. with beginners keeping coins on exchanges until they start to get to higher numbers, such as $500, $1k or even more, and then once you get to those higher amounts, then you should be figuring out ways to move some or all of the BTC that you have on exchanges to private wallets. In recent times, it can be expensive to move a bunch of small BTC transactions.
I agree, anyone who is buying Bitcoin on a small scale should kept their BTC in the exchange itself because withdrawal fees are insane due to market congestion which is an ongoing issue since Nov so obviously the withdrawal fee on most exchanges are around $40 so I wouldn't withdraw unless I have around $500 or let's say once in a couple of months for someone who is been investing using DCA every week.
Withdrawing via LN is an option but definitely I won't recommend it for a beginner because they could mess up with opening LN channel and lose their BTC, so the good choice is keeping funds in exchanges but not for too long as well.
If after starting small scale investment an investor feels that he will increase his investment amount regularly then he must keep his investment in any exchange account. An investor will invest regularly and an investor will invest a large sum of money together but there is a significant difference between these two investments. An investor who will invest a large amount of money together will not need much to transfer bitcoins, but an investor who will start investing in a small scale and will continue his investment regularly will definitely need to transfer bitcoins regularly. In the case of regular Bitcoin transfer, it can be seen that due to high transaction fees, he is not able to make regular Bitcoin transactions, as a result of which there is an obstacle in his transaction, so that there is no obstacle in the transaction, consistent investors are advised to use an exchange account.
Many may say that holding bitcoins in an exchange account is risky, you are not the only user who is holding their investment in an exchange account, there are much bigger investors than you who have left millions of dollars in exchange accounts. Since they took this risk, you must also take risks, and without taking risks, progress in life is not possible.
You are confusing the Bitcoin investor with the Bitcoin trader, here I am talking about the investor who deposits fiat to exchange then buys BTC and keeps repeating it every week/month for a long period let's say 5 years straight who should be termed as an investor and for them there is no need to keep withdrawing their BTC from the exchange other than the security concern if exchange hot wallet hacked and users lose their funds.
A bitcoin trader is someone who keeps moving crypto around exchanges so they can make profits with the price difference from one exchange to another and numerous other ways.