I used to, but just having safe usage practice (don't load from un-trusted sources), I have never had and issue, My last 4 phones I disabled it right away, better battery life and faster performance.
I've never gotten any kind of malware on my phone. I'm pretty careful what apps I load and where I browse. I'll almost certainly disable Lookout, but might re-enable once a month and run a scan, then disable it again.