The Hindu theology is based on the theory of Karma or fate. The good and the bad acts by you have a positive or negative effect on your soul. This balance sheet of your Karma is carried forward from life to life. It is based on this that you have good and bad experiences in your life and sometimes in the next life.

According to the Vedic scriptures and the learned saints, performing mantra-japa, stotra recital, dana, pooja/homa etc. are auspicious as they produce positive effects and counteract and remove or at least reduce the negative Karma and improve your life.
The poojas and homas work when performed properly reciting the prescribed mantras, using the prescribed ingredients, by making the required homa sacrifices and doing the prescribed dana etc to the pundits. Unfortunately a lot of people and pundits perform them either to cut cost or time and the results are not what you expect.

To counteract the negative influences of the planets and their bad yogas/doshas, or to improve and attain various desired objectives, the scriptures have prescribed several poojas and homas of various deities. The deity is worshipped in the prescribed ritualistic manner with mantras and offerings, the Brahmins are given anna-dana, vastra-dana and dakshina etc. The positive influence of these give you positive results. You experience better results and get an inner strength and confidence. Sometimes the results are instant and sometimes they are slow. But they are certain. I say it with confidence because poojas have vastly improved my life.