I'll say it one more time.
Submitting chat logs not a requirement, they do not demonstrate a relationship. For all the ECO knows, the logs could have been recorded/forged by the applicant and a drag queen in Kabul. We have enough problems verifying the authenticity of bank statements and tenancy agreements, much less chat logs.
But worse still, chat logs are read with a dispassionate and critical eye. So the comments, "...I spent the whole day waiting for you to come online..." or "...I can't wait to get married..." or "...I can't wait to live in England..." or "...How long does it take to get the visa..." can all backfire with devastating effect.
I have true cases in my archives where innocent banter was misread and caused harm to the applicant. It has screwed up people's lives. So if somebody *INSISTS* that they cannot substantiate a relationship without chat logs, then at least let a dispassionate reviewer examine them first.
As a personal note, the most convincing evidence of a substantive relationship is drawn from the real world rather than cyberspace.
To be fair, many people have submitted chat logs and it was fine. Just take it to mind that there's risk and a big-time downside if it backfires...