We should connect the electric appliances in parallel to household circuit because :
i) Each appliance gets the full voltage.
ii) The parallel circuit divide the current through the appliances. Each appliance gets proper current depending on its resistance.
iii) If one appliance is switched on/off other are not affected.
If appliances are connected in series the following disadvantages are arised :
a) Same current will flow through all the appliances, which is not desired.
b) Total resistance becomes large and the current gets reduced.
c) We cannot use independent on/off switches with individual appliances.
d) All appliances have to be used simultaneously even if we don't need them.