Security professionals now generally recognize that siloed security tools and systems have undercut efforts to find active attacks more quickly and efficiently. SIEM was created over fifteen years ago to integrate security data for providing real-time analysis of security alerts generated by applications and network hardware. The principle is similar to one of the early computing maxims of garbage in, garbage out. These systems can only be as good as the data they ingest. Getting data in real time or near-real-time is important.
Source: https://www.helpnetsecurity.com/2021/05/31/rethinking-siem-visibility/