I don't own guns with manual safety levers, however I do install NY triggers on all my Glocks, which I view as essentially being a safety. The same with my DAO revolvers with their long, heavy trigger pulls.

The reason for any safety is its namesake... safety. Preventing unintentional discharges. No one is perfect, we all can make mistakes. Any possible tactical advantages are relatively far fetched outside of law enforcement and even then the cons outweigh the pros as far as I'm concerned.

The reason I prefer a heavier trigger rather than a lever however is that I do believe a manual safety lever could potentially interfere with my ability to respond no matter the depth of training. Numerous instructors have reported seeing even very seasoned shooters fail to get the safety disengaged on their 1911's in Force on Force training. I have seen it as well, primarily with little pocket pistols with small safeties during ECQ FOF. It can often be difficult enough to effectively access a weapon from a pocket when engaged in a contact scenario, let alone positively get that tiny safety disengaged.

Thinking you can simply be proactive and rely on situational awareness is not an effective strategy IMO. The possibility of having to respond in a reactive close-quarter defense situation remains a realistic possibility no matter how alert or aware you happen to be. Understanding counter-ambush methods are extremely important. I'm sure many think the safety will pose no issues at all in these of encounters, and it very well may not, but relatively few have tested it thoroughly in reality-based training.