Happiness is one of the most important factors in this game. Happiness makes your workers and army live for a longer period of time. Even if we you are going to buy a 2 months worker for gold, he will live as long as your happiness level will let him. Happiness also gives you an opportunity to sell your resources and workers; you won't be able to do that without it. To sell resources you need only 60% of it, but to sell workers and army you have to reach 100%. To have 100% of happiness all of your houses have to be 10th lvl - even one house on 9th lvl will make your happiness less. For example, you have 5 houses 8th lvl, 2 houses 7th lvl and 4 houses 2nd lvl. Your happiness will be 40+14+8 = 62/12 = 52%. To count your happiness level, you have to add summary lvl of your buildings and divide it with the amount of your houses. This is very easy to understand but would be best if you would make all of your main houses (6) lvl 10th and then think about building new ones. Using this method you will save some money on workers and improve your city much faster. (TO SEE IN WHAT INFLUENCE HOUSES HAVE TO BE GO TO THE xxx ARTICLE AND CHECK IT)