[ben1040]

It looks like the main reason to pay is for data retention -- otherwise the free service only gives you 24 hours of data. IIRC that was also the distinction between the previous services New Relic offered, free for 24 hours, pay for more.

[vehementi]

Old (?) free accounts did not have full analysis tools - you could not break down slow requests etc. with Java monitoring, only see the average response time over a time range.