The gemara cites a machlokes between R. Yochanan and R. Yehoshua Ben Levi whether the concept of לסמוך גאולה לתפלה, applies only by day or even by night. R. Yehoshua Ben Levi holds that it doesn't apply at night since the primary redemption was during the day, not at night. What is the purpose in being מסמיך גאולה לתפלה and why is one who does it deserving of the title בן עולם הבא? Rabbeinu Yonah says that Hashem took us out of mitzrayim to be His servants. We recognize this in the bracha of ga'al yisroel. By davening immediately afterward we show that we recognize that we were acquired from Mitzrayim by Hashem to be His servants and are bound to his mitzvos. Alternatively, Rabbeinu Yona writes that it is Hashem earned out full trust by taking us out of mitzrayim and we are completely confident that he will always provide for us. Therefore, we say that just as we had this confidence when we left mitzrayim, we maintain this confidence when we turn to Him to ask for our needs.
Both approaches of Rabeinu Yona seem to attribute the advantage of being סומך גאולה לתפלה to be something new. It is not that the bracha of geu'la compliments the tefila, or the tefila compliments the bracha, rather the connection implies either a recognition of being his servants, or confidence that He will provide for us. Rashi seems to offer another explanation by citing the Yerushalmi which says that by making the bracha of geu'la and then walking away, we are tantamount to servants who knock on the door of the king and run away when he answers. After we appease Hashem and speak great praise about how we were redeemed, we run away without asking for our needs. Rabbeinu Yonah seems to say that both the bracha and the tefilla serve a significant function on their own, but when we put them together we show a special allegiance to Hashem. Rashi on the other hand says that the reason we need to daven after making the bracha of ga'al yisroel is because otherwise the bracha doesn't fulfill it's purpose. Rashi seems to say that the entire purpose of ga'al yisroel is to set up a situation where we can ask Hashem for what we need.
The gemara asks that according to R. Yochanan who requires geu'la to immediately precede tefillah, how can we say the Bracha of השכיבנו at night which separates between the bracha of ga'al yisroel and tefilah? The gemara answers that השכיבנו is like a "long geu'la" - meaning that it is an extension of the bracha of ga'al yisroel, and therefore not a separation.
Tosafos explains the concept of כגאולה אריכתא דמי to mean that since it was instituted by chazal, it is not considered to be a hefsek. It seems that Tosafos holds that only personal interruptions are viewed as a hefsek. Based on this, Tosafos holds that the insertion of יראו עינינו and other pesukim are also not considered a hefsek since they were instituted by the chachamim.
Rabbeinu Yonah seems to disagree with Tosafos. Rabbeinu Yonah explains that השכיבנו is considered an extension of the geu'la because it is a reference to the night before we left mitzrayim and Hashem protected us during the makas bechoros. Rabbeinu Yonah seems to hold that simply being instituted by the chachamim doesn't give it the status of גאולה אריכתא. Perhaps it is for this reason that Rabbeinu Yona cites the Ramban disagreeing with Tosafos, that יראו עינינו shouldn't be said because it does interrupt between the geu'la and the tefillah. Even Rabbeinu Yonah himself who justifies the saying of it, is only because ma'ariv originally started as a re'shus where it wasn't so important to be מסמיך גאולה לתפלה, but otherwise would hold that it couldn't be said.
Perhaps the machlokes between Tosafos and Rabbeinu Yona regarding יראו עינינו being a hefsek, is actually dependent on the function of being מסמיך גאולה לתפלה. Rabbeinu Yona who holds that it is a special statement that is implied from the immediate juxtaposition that we show allegiance to Hashem or confidence in Hashem, it is only implied by an immediate juxtaposition without any other interruption. Therefore, Rabbeinu Yona is litshi'taso that even a hefsek instituted by chazal would dilute the connection between geu'la and tefilla so that the concept would no longer be recognized. However, Tosafos holds like Rashi that the purpose of being מסמיך גאולה לתפלה is that we can't walk away from גאולה without asking for our needs since that is the entire purpose of why we mention the geu'la. There isn't anything that we are trying to imply by the connection, but by breaking the connection we are undermining the purpose for the bracha of geu'la in the first place. Therefore, anything that chazal institute to be there wouldn't be considered knocking on the door and walking away. The immediate juxtaposition is only necessary for Rabbeinu Yona who holds that the effort for one to follow the other has a special implication, which wouldn't be obvious if there were some other passage in between. But Rashi and Tosafos hold that the concern is that we shouldn't knock and run, and any passage instituted by chazal would not qualify as running away after knocking.