Is it safe to use an address twice (privacy excluded)?
Is this really a problem in practice?
If you say, you don't care about privacy (privacy excluded), you can use a same address many time. It's address reuse.
It practically is not good for your privacy and in order to get better privacy, you need to use Bitcoin change addresses.
Some advice is here
https://blockchair.com/bitcoin/privacy-o-meterGeneral guidelines for sending BTC transactions
Blockchair can not help you improve the privacy of your transactions but here are some basic recommendations on how to stay anonymous on the Bitcoin network
Don't send round numbers
Don't send round amounts. Instead of sending 0.1 BTC, send 0.10125
Use Bitcoin Mixers
Mixers add an additional layer of privacy to a transaction to avoid exposing user identities.
Avoid reusing wallets
Don't send your Bitcoin change to the same address you use for sending bitcoins.
Avoid including many of your addresses in one transaction
Any time you can, try not to send BTC from your various Bitcoin addresses.
Avoid using "send everything" option
If you are withdrawing funds from an exchange, it is okay.
If you're moving funds to another wallet, do not transfer the whole amount to another address. It greatly compromises your privacy.
Spending your Bitcoin