I speak from experience when I say that insulating your home is life changing. Insulating helps maintain a comfortable living environment by maintaining inside temperatures and simultaneously reducing energy costs.
The main purpose of insulation is to create a barrior around your home which reduces the amount of heat entering the home on a hot day and also reducing the amount of heat loss on a cold day. Since most heat is lost or gained through the roof and exposed walls, these are the core places to insulate in order to create a comfortable living environment.
The reason your home gets warm during the summer despite your use of the air conditioner is due to the concrete, bricks, and other materials heat capacity. As they get hotter and hotter they start to emit this heat into your home. The opposite happens in the winter where the heat from inside your home gets absorbed by the roof and walls and emitted outside.
In a home with good insulation heat loss through the roof and walls is very limited. This allows the temperature in your home to be comfortable with much less heating or cooling. This being said, insulation is not magic, depending on where you live, you will still need to use heaters and air conditioners but they will not have to work as hard. Insulating your home can reduce your heating and cooling costs by up to 40%. This means massive savings on energy bills for you and a lot less pollution for our planet. I just had my insulation done 2 months ago and I am already seeing a huge decrease in my energy bill and a huge improvement in my comfort!
Insulation is only one step in creating an energy efficient home. Other things to look at are windows, doors and floors for air gaps. Having windows tinted or covered with thick curtains definitely helps. Having draft stoppers on your doors will also make a difference.
Generally the cost of insulation runs between $1 and $1.50 per square foot though costs do increase depending on the type of insulation you get.
It took me years to finally decide to get insulation and now that I finally have it I could kick myself for not doing it sooner. While it may seems like a big expense it is actually more of an investment that you recoup quickly just by having your energy bill shrink. It has made a world of difference in my home and significantly improved my living conditions, it could improve yours too.