God is not a man that He should lie and there are benefits to agreeing with what He says. There is power in agreenemt. When you voice your agreement with God certain things take place.
1. You kill the root- The curse and all the works of the devil are rooted in the spiritual so to get rid of it or change it you have to attack it at the root. If you kill the root then the fruit has to die. And the word of God is a sword (Ephesians 6:17). So when you voice your agreement with the word you are cutting the roots of that evil in your life and at some point it will have to go.
2. You sow seeds- The word of God is seed (Luke 8:11). And your spirit is soil (Mark 4:26-28). And the word also performs as water or rain (Isaiah 55:10). So when you voice your agreement you plant and water seed and you will get a harvest. 1Peter 3:10 "For he that will love life, and see good days, let him refrain his tongue from evil, and his lips that they speak no guile." Notice if you want to see good don't speak(sow) evil. Because when you say you sow "The word is night thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach" (Romans 10:8).
3. Faith comes- "So then faith cometh by hearing, and hearing by the word of God" (Romans 10:17).
4. Gives substance to your hope- "Now faith is the substance of things hoped for, the evidence of things not seen" (Hebrews 11:1). Faith gives substance to your hope like an apple seed gives substance to an apple. That's why Jesus said several times "If you have faith as a seed... .
5. Your words accomplish- God said, "So shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall accomplish that which I please, and it shall prosper in the thing whereto I sent it" (Isaiah 55:11). So when your words are in line with his words then they accomplish.
6. You receive his will- When the angel told Mary she was going to have a baby she continued to ask questions. And it was only when she agreed with him that the angel left (Luke 1).
7. It establishes the word in your life- "In the mouth of two or three witnesses shall every word be established" (2Corinthians 13:1). So you establish the word in your life when you voice your agreement with God.
Those are just some of the reasons for agreeing with God. So, be patient for by faith and patience you inherit the promises of God (Hebrews 6:12).