The main reason to keep your battery on a tender is to keep the plates from sulphating (sp?) This is basically a coating of a Sulphur on the plates and will eventually lead to the lower CC's on your battery and it's death. This occurs as the battery slowly discharges, EG the electrolysis that makes the batteries power possible in the first place through the dissimilar metals and the electrolyte. As the battery discharges the electrolyte's ph and specific gravity changes as well. That's why the best way to check a batteries level of charge is with a hydrometer, but, you can't do that with these little sealed batteries so you have to go by voltage.
12.7 vdc is considered a 100% charge, 12.5vdc is 75% charge and is supposed to take 4 hrs at .5A to charge it.
Anyway, the Battery Tender type of charger keeps the voltage up at what in considers 100% charge, once it drops below that voltage it goes into a charge cycle, at a max of .75amps. The other thing that the newer versions do is, as it is charging it varies the voltage up and down, or what is known as peaking. This helps to clean the plates in the battery as it is charging.
The expected service life of a YTZ7S battery is roughly 3 years, I have gotten 4 out of mine, and that was before I put it on a battery tender all the time. When my battery went bad, with no load it showed 12.5 volts, but as soon as you hit the button it dropped to about 8 or 9 vdc. That is the result of heavy sulphating of the plates, enough plates to produce good voltage, but, no volume or CC's.
So this is my long winded opine to keep your bike on a battery tender all the time.