You could send transactions instantly, as 0conf transactions were considered secure far beyond a reasonable doubt for small transactions.
For large payments ie buying a car or a house its best to wait for confirmations
This is still the case in Bitcoin Cash, due to not having "replace by fee" which added by blockstream terrorists and removed the security of 0conf transactions in 2015.
0Conf is the Achilles heel of Bitcoin (BCH) and anyone who doesn't agree has a fundamental misunderstanding of how it works, and why it is so lucrative.
https://www.youtube.com/watch?v=rZjasKZC7p0&t=4s