When would you need to go about getting a turnstile? It is a fairly simple answer: you would need a turnstile whenever you are having a major event where you are going to have a ton of people going inside into one location. Say there is a state fair going on at a certain venue, or part of the fair, and you need to make sure you have the appropriate ways to check people and make sure they are paying for their tickets before getting in. While you can set up some random type of barrier or entry point, it is much easier when you have turnstiles.
What we suggest is that you look into turnstile rental in a situation where you are not going to need the turnstiles on a regular basis. The cost of a turnstile, in terms of buying them, is fairly high, and you do not want to go into such an expense unless you know you will need the turnstiles all the time. And even if the venue is going to need them all the time, you may want to stick with a rental for the first few months to keep your costs down. When you have more capital, you can make a purchase.
In terms of how they operate, turnstiles come in a few different styles. Some of them are even locked, and the person can only turn them if the person at the other end presses a button. But most of the ones you get are not locked in such a way. They will be open and people will have to pass through them normally. But they do help you slow down the traffic at a spot, because you cannot really have more than one person going through the turnstile at the same time.