I recommend installing some kind of switch, and be sure you maintain some kind of kill swtich. Otherwise you won't be able to turn off the bike in a panic situation.
On one bike, I installed a rocker switch and hid it just under the seam of the gas tank. I would reach down to turn the bike on with this hidden switch. This was great till the day the top popped off the carb leading to WFO throttle. The bike leapt forward, I pulled in the clutch, and as the bike revved to the moon I pulled over, had to gingerly get off the bike to the left, and use my right hand to reach down to my tank's left side to get to the switch...it was sketch. Always keep a handlebar mounted kill switch of some sort.
Also, you need to have some kind of master on-off switch; that could be your kill switch as well. But don't settle for just a pushbutton kill switch with the master left always on. The reason is a passerby or child will someday press the red starter button (if you bike has electric start) and the bike will launch if it is in gear. If your bike is kickstart only then this is not an issue and you can just dispense with any kind of switch and twist the wires together.