I have not heard anyone say that with a lot of input, and without any output, you can just start speaking and the words will flow out of your mouth like beer at a pub after a British football match.
To speak well, you need to speak, and you need to speak a lot. If you understand well, as tony and Helen say they do, then you are ready to do a lot of speaking, and really need to do so in order to achieve full fluency. If that is not readily available to you, you can continue to improve your speaking potential by listening and reading, but you eventually need to speak. If you have limited opportunity to speak, write, and then have it corrected, and then read the corrected text out loud ten times. This is what Hermann Schliemann did so successfully many years ago. (google it)
As to cyclists, learning a language is much more difficult, takes much longer, requires the acquisition of lots of words etc. The similarity is in the need for confidence and motivation to do both. A person who has seen others ride bicycles, like his or her siblings, will consider it a normal thing to do, want to do it, and will learn more quickly than someone who sees a bicycle for the first time.So it is with speaking languages. Confidence, and exposure help tremendously . Listening and reading not only build vocabulary and familiarity, they build confidence. But you still need to speak, and work your way through the initial difficult period, while continuing the input activities.
As alexandre says, when you speak you are confirming what you think you know about the language, and identifying your gaps. This supposes you know something. When you are a beginner you know very little if anything, so to me, the benefits are limited.
If you have the time and money to sit in a one on one classroom, you can learn from scratch while conversing, or taking lessons, with a teacher. If you have limited money and time, you are much better off building up your vocabulary and familiarity with the language using your own free time, or dead time, listening over and over, reading, reviewing words and phrases until you are just dying to try these out in conversation.
You will speak when you feel up to it, and when the opportunity presents itself. That point will vary from person to person. Just as the child does not speak fluently as soon as he/she starts speaking, and stumbles often as he/she ramps up in speaking, so with the adult. The more you have read and listened and the broader your vocabulary the better your speaking will go.