No one should ever have a reason to put brake fluid into a car unless
they are swapping/exchanging fluid or they have recently repaired or
replaced a component that carries brake fluid (like a line, caliper,
wheel cylinder, master cylinder etc.. basically anything but the
pads/shoes). If you ever feel inclined to add fluid because you are
close to the min line or lower then normal, you may have a problem that
needs fixed and will only get worse. As the brakes wear, the fluid
level will go down as the brake fluid displaces the distance of travel
that the calipers or wheel cylinder is extended at rest. This is normal
and the reason for a "max" and "min" line labeled on the reservoir. The
level will always go back up when the pads/shoes are replaced. If not,
check for a leak and get it fixed. I have never seen a leaking brake
part not get worse and degrade quickly. More often then not, the
leaking fluid will contaminate the stopping surface rendering it useless.
On a related note, removing the fluid reservoir cover makes it easier to
drive the caliper pistons back in with the C clamp (If you added fluid
prior to this though, it will overflow

) and using the old pad turned
over against the piston saves you from scratching or marring the piston
surface with the clamp.