New plants and sod need to be watered regularly until they are established. Unless there is regular rainfall, this means watering 1 -2 times per week. Plants on the south or west side of the house will need to be watered more than the east or north side, and lawns need water to be healthy and compete with various weeds.
Climate is changing- summers can be very warm and dry. If you would rather be at the lake or golfing than dragging a hose around your yard, you should consider installing irrigation. Irrigation ensures that your plants will get watered. It doesn’t mean you need to use it all the time, but when you need it, it is there. You can also be very efficient with water using an irrigation system. A properly installed system reduces overspray and will water when there will be less evaporation.
The type of plants you have will determine how much you need to water as well. Some shrubs and perennials like quite a bit of water, but all plants require good drainage away from roots as well. Unfortunately the symptoms for over watering are similar to under watering. Your plants can drown if water cannot get away from roots so ensure you have good drainage.
Regular water and good drainage provide a sustainable environment where your plants will thrive.