Having the battery at 100% and charging constantly can reduce lifespan of it so conservation mode just limits it to 60% to counteract that problem. It does not harm the laptop, quite the opposite really. If you want to unplug the laptop to bring it around somewhere you may want to turn conservation mode off before doing so to allow it to reach 100%.
Basically as long as you keep the laptop plugged in all the time, conservation mode is recommended.