I have never searched my message text history with the exception of trying to find images sent to me. Never content. Most companies I’ve worked at have a similar policy of not archiving text messages from internal chat. No reason to keep content, minimizing the amount of data you archive is a core element of security and risk mitigation for a number of reasons. Plenty of large organizations don’t archive employees Lync/internal chat messages for similar reasons. And from a threat perspective you don’t know ahead of time what information an attacker will find useful.