Warning: This address is being reused

[10_sjdovn_10]

Hello,

I imported a wallet in electrum so, a receiving address and no change address.
when i wanted to make a request using the address, a warning message says This address is being reused

What happen for example if i send half amount of bitcoin, and no change address exists?
Why addresses should not be reused?
Why a transaction splits into outputs?

I hope you understand my words 

[jackg]

If you care about privacy, you shouldn't reuse addresses. If not you can.

Wallets generate a new address every time one is used to that your coins stay more pruvate. There are options in electrum to either enhance things for privacy or enhance them for lower fees (I think it's in preferences).

[Charles-Tim]

I imported a wallet in electrum...

You can not import a wallet into a wallet, you can only import wallet file, seed phrase or private key into a wallet.

What happen for example if i send half amount of bitcoin, and no change address exists?

Change address will always exist on reputed noncustodial wallets like electrum. If you send half of your bitcoin, the half you sent will be sent to the address you sent it to and be confirmed while the UTXO will automatically be sent back into another address on your wallet.

Why addresses should not be reused?

For privacy reasons.

Why a transaction splits into outputs?

This question is not clear, but if it is what I guess it to be, as explained above, that the first output will be sent to the receiver/recipient address while the second output is the UTXO that will that will be sent to an address on your wallet.

[hosseinimr93]

What happen for example if i send half amount of bitcoin, and no change address exists?

If you imported a single private key and now your wallet includes a single address, the change will be sent back to the address you are sending from.
If you imported a seed phrase (a series of words), now you have a HD wallet and the remaining balance of UTXOs selected by electrum will go to your change address.

Why addresses should not be reused?

As long as your privacy doesn't matter to you, you can reuse addresses.

Assume that you gave me an address, so I can send you bitcoin. Now I know that address belongs to you.
I can easily know that every fund sent to that address either in the past or in the future is owned by you.

Why a transaction splits into outputs?

UTXOs must be spent totally.
Assume that you received 1 BTC in a transaction and you want to spend 0.4 BTC of that.
You cannot send 0.4 BTC without touching the other 0.6 BTC.
So, your transaction must have at least two outputs. One of them will receive 0.4 BTC and the other one (your change address) will receive 0.6 BTC - fee.

Change address will always exist on reputed noncustodial wallets like electrum.

If you have imported a single address using its private key (which seems to be the case here), there won't be any separate change address and electrum will use the sending address as the change address.  

[HCP]

What happen for example if i send half amount of bitcoin, and no change address exists?

In Electrum, the remaining half just goes back to the single address that your wallet contains. In other wallets, sometimes they would automatically just generate a new random change address for you. This behaviour often led to the loss of funds from paper wallets if users were not aware of what the wallet was doing with regards to handling change.

Why addresses should not be reused?

https://en.bitcoin.it/wiki/Address_reuse

Why a transaction splits into outputs?

Maybe try this: https://en.bitcoin.it/wiki/Change and this: https://en.bitcoin.it/wiki/Coin_analogy

[Pmalek]

Ensure that you don't make mistakes when importing to Electrum, so you don't create a watch-only wallet instead of a regular wallet. As long as you have a copy of the private key of that watch-only wallet address, you will be fine, but if you delete its private key, any funds sent to that address can't be spent. Import only private keys or recovery phrases if you intent to spend from those wallets.