YoungKopernic, you have an pwm controller which is basically a switch. On at a predetermined voltage, if sun is out, and off at predetermined voltage, battery charged. This system works, but isn't best for your batteries. A mppt type will get you more power from your solar panels and usually a 3 stage charger on the better controllers.
You will reduce the lifespan of a set of deep cycle batteries if you don't use a 3 stage charger. I can't say by how much as there are other factors at work, but it be reduced.
As for cycling the battery, charge & discharge, every cycle wears on the battery components. A little. A true deep cycle battery is built to take it though. Unless you seriously discharge a deep cycle battery, like to 50-60%, you won't notice a reduced lifespan by daily charging with a proper charger.
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.