For an on-prem general purpose logging server, it's fast and easy to maintain. The query engine supports fairly complex queries. Did I mention it's fast? Plus it's an industry standard so it's an easier sell in the enterprise. It's also actually not that expensive at low data volumes -- prices are comparable to Sumologic.
Cheaper alternatives? You can roll your own logging server with fluentd and a database. Some folks will recommend elasticsearch, but we tried it and it was challenging to set up just right.