The short answer is that if one attempts to use a micropipette for volumes above or below what is indicated the volumes dispensed may not be accurate, and for volumes larger than indicated you could damage the micropipette.
Micropipettes are lab equipment designed to accurately measure extremely small volumes of liquids, measured in microliters (1/1,000,000 of a liter). There are some micropipettes that measure out only one volume, but most are designed to be able to eject within a range of these very small amounts, using a dial. These pipettes are calibrated to be accurate only within the range indicated--this range can usually be found on the micropipette itself, generally on the top of the plunger. When micropipettes are used in experiments in research labs, they are checked frequently to ensure they are still accurate, but that accuracy is only within the range indicated.
If you attempt to "dial up" the micropipette to a volume greater than the maximum indicated for that instrument, you could end up drawing the fluid up into the micropipette itself, rather than just the disposable tip. If fluid enters the micropipette itself, it can be contaminated or seriously damaged, possibly beyond the point of repair. As they are expensive and frequently used instruments one should take great care to treat them properly.