It's okay having discussions on users' talk pages, or on the forums. However what is not allowed is the deletion of said discussions. This can break up a conversation and derail the topic of forums, plus on talk pages may hide warnings that can lead to you getting the wrong block or similar punishment. Users who delete talk page messages or forum posts without prior consent risk a warning or even a block if caught. However, if a message is blatantly vandalism, this policy does not apply in lieu with BN:IAR.