Many apartment and condo dwellers find that cutting the cord can be a little tricky IF conditions aren't just right for reception.
Building Material Blockage - Part 1: Stucco, concrete, metal awnings, fire escapes, metal molding, all of these things can impede reception so an antenna would need to be in a window in order to have a chance with these conditions. Which brings us to building blockage.
Building Material Blockage - Part 2: Many apartment or condo dwellers find that the higher the unit the better the reception. This is all dependant on the signal strength in the area and the location of the unit in relation to the transmitting tower. If the signals are transmitting to the south side of your location but you only have a window that faces the opposite way you may not get as many signals as you would with a southern window placement.
The signals are weakened because they have to travel through the building materials to get to the antenna and often will not be obtainable. In some apartment/condos customers get many channels in one side of the unit and little to no channels on the other side. When possible placing the antenna in a window that is facing the direction of the towers for optimal reception chances.
This theory is true with any location where you use an antenna. We have some customers that get tons of channels with an indoor antenna on one side of their home but only a few using the exact same antenna on the opposite side of their home. When there isn't a clear line of site to the towers and the signals have to work their way through building materials it can be very difficult to have perfect reception success.