Well I can speak for myself personally on this one, if it helps a little
The Bible says “the prayer of a righteous man availeth much” and also that we should build one another up in prayer…that we have “a cloud of witnesses…” Mary, being the perfect model of obedience and faithfulness to Christ, is the best advocate we have

I could ask my neigbor or my brother to pray for me (and I should) but I should also ask my mother to pray for me… Jesus hears our prayers, and whatever is close to the heart of Mary is also close to His heart.
Think of the wedding feast in scripture… Mary came to her Son and told Him there was no wine… Why did she do that? Of course He knew there wasn’t wine…and He didn’t need His MOM to tell Him… He asked her “woman, why does this concern me? My Hour has not yet come…” And She told them “Do whatever He tells you.” As she continues to tell us today!
Even though His hour had not yet come, Jesus took the request of His mother especially to heart… She still obeyed Him and accepted His will whether it was what she asked for or not…(which is what WE as Christians should all strive to do!)… And because of the humble, faithful heart of His Mother, Jesus turned the water into wine!
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The key though..is not to get into the mindset that "well if I ask mary to pray for me...then Jesus will do whatever I want!" Rather.. I am humble, and unworthy to ask this....I will pray with my Mother, the Mother of God, to help me come before Christ with the desires of My heart. But I will still concede to do "whatever He tells me" ...His will before my own.
Also… personally, devotion to Mary has deepened my love and devotion to Christ so much! By accepting her as my Mother, I feel connected to her Son in such a close, familial way. It’s no longer an abstract, spiritual, undefinable relationship… But rather, my relationship with Jesus feels like He truly is a part of my family, that I have been adopted and joined to Him…Understanding the role of Mary my mother and growing in devotion to her has tied me to Christ so much more than I ever felt as a protestant

I wish I could explain it a little more clearly… But Mary, for me has been the “key” to growing in faith and love… She is truly a gift and a blessing! God knew we needed a mother!