I also run my bike in the reserve position. As Ben said, water and impurities built up in the bottom of the tank may prevent you from using the reserve just when you need it. I usually watch my trip meter and fuel gauge and fuel up when I am down to about 1/4 tank. Also monitor the accuracy of your fuel gauge and you will learn when to fuel up. I have found that when the red low warning light comes on on my bike, I have one gallon of fuel left, so its time to hit a gas stop. I also know that my bike gets about 42 to 45 MPG, so that dictates how far I can go before running out of fuel. I have actually gone 52 miles after the warning light comes on but that was at reduced speed. When I filled the tank and did the math, I had 1/10 of a gallon left in the tank. And I have only done that once. I usually try to stop right away, usually within 10 or 20 miles.
As an experiment, fill a two gallon can and strap it to the back seat and put your petcock valve in the ON position and ride it till it runs out of gas, then move it to RESERVE and keep riding until you run out of gas again and you will know how far you can go on a tank of gas. Keep track of the mileage each time you run out of gas. Refill from the two gallon can and look for a gas station.
Also keep in mind that speed, headwinds, a passenger, and hills or mountains will decrease you mileage so take that into account. I pull a camper and I only get 36 to 38 MPG at 60 to 65 MPH. So that requires me to stop about every 150 miles. Which coincides with my need to take a bathroom break! At 75 years old the bathroom breaks are getting more frequent!!!
JIm