Have you ever noticed that most thermostats are in hallways, not far from a return vent?
That is because a central location tells the thermostat what the median temperature is in the home; you know, about what the middle temp is throughout the house. Second, if it is nearer a return vent than a vent that has hot or cold air blowing out of it; you are getting a temp that is truer to what people in the house feel. If you place it in a room near an extremity of the house, or near a heat source or cold air source, your system really won’t get a true idea of how well or poorly it is doing.
A couple of factors that might affect the placement otherwise, might be the presence of other air conditioning or heating units in the house. An experienced air conditioning or hvac professional should be able to look at your system and give you something more specific for your home.