It is important to know and understand that an LDO does this by "burning of" the excess voltage and this can and does result in quite a lot of heat which must be handled in the design. The amount of energy burned off is easy to calculate. Let's imagine using a 3.3V regulator from a 5V source. The voltage drop over the regulator is 5V - 3.3V = 1.7V. If using 100 mA that would result in 1.7V * 0.1A = 0.17W (or 170 mW) of power.