I rotate my Tender between two bikes and my wife's scooter. The wall-wart is positioned so I see the light when I walk out to my garage in the morning and remember to switch to the next bike. In the summer when I'm riding more, I just rotate between the Harley (rarely ridden) and the scooter.
I use my battery tender every night during the winter since it often gets down to single digits for the low, or -10 to -20 degree Celsius. During the spring, summer and fall, no.