Many people purchase a dehumidifier due to a visible damp problem, mould growth, damp walls and floors, condensation on windows etc. They do this without actually knowing what the relative humidity is within the home.
Purchasing a Thermo-hygrometer will provide you with an accurate temperature and relative humidity reading, therefore enabling you to set your dehumidifier to the correct setting if you have a manual control on your dehumidifier.
Using a Thermo-hygrometer will enable you to check conditions easily within various areas of your home, helping to identify problem areas.