No adverse effect on battery life. Apps running in background (not actively used) consume insiginificant battery.
If set properly, it will increase battery timings on standby slightly, because LED will not blink for unimportant notifications.
Like using the same app, from advanced setting i have enabled sleep timer, so the led does not blink in my sleep time. After sleep timer, fully charged battery stays 100% or 99% even after 8 hours of standby (sleep time).
Before, constant led blinking consumed maximum ~5-10% charge on standby in for 8-12 hours.