Searched our forum, didn't return any results. Thought these might be useful to those keen on avoiding the spark between the lipo and esc positive connector, caused due to immediate high current capacitor charging.

http://www.rcgroups.com/forums/showthread.php?t=935350
http://www.rcgroups.com/forums/showthread.php?t=987819&page=5&highlight=sparking#post13518334

Any other thoughts...

I have always had a little spark, but everything still runs fine, does it has any side effects?

Yes, we all will witness the spark,the intensity of which depends on the battery's capacity.
6s and above, it's really visible and with a whack sound.

I presume, no significant harm in the short run as long as your connectors are good quality.
Poor connectors blacken due to pitting very soon and heat build up will increase. Has happened to me on a 6S, 2650mah blue lipo 'cos my bullet connectors weren't that good. Even the housing got a dose of this spark and started melting slightly with use.

The preventive resistor just limits the current charging the capacitor and hence curtails the spark or the arc.