It depends on how functional you are. Lots of people present with suicidal ideations but it doesn't mean they get sectioned. Many live normal lives and are suicidal. It's not a black and white thing. Some people are severely mentally unwell and yet they are all around us and we probably wouldn't even realize without taking a deeper look. Whether it does mean people get sectioned or not is up for debate and it's pretty controversial because of how it can be both a good and a bad thing, depending on how effectively psychiatric services respond to the threat. Some people talk about suicide and slip through the net. Some people don't talk about it but they get sectioned because of the current state they are in.
Ultimately, they can't stop suicides. And in the UK, where you are from judging from your location status in your profile, NHS psychiatric services are so overwhelmed they cannot keep those that truly are a suicide risk for all that long. My friends father was sectioned for all but a weekend and if he said to them that if he was released he would kill himself and they let him go. He killed himself and his son found him the next day hanging in his home. That's just one story.
The best advice is talk to them, keep talking to them, keep them in the loop all the time and be honest and most importantly, challenge them when you feel like they may not be taken your mental health seriously. They are so busy and their resources are so finite that their duty essentially is to minimize overloading of the hospital beds and juggle who they believe at the time to need the most support. They get that wrong a lot of the time and people get hurt or even die. You need to make them aware of everything and make sure you are pushing them to do their job and acknowledge the severity of your issues. If you feel like they are not you can escalate things and at this point things are on record and so they cannot deny the interactions you have had and the support you have told them you need. Many people don't believe they have a voice and so they don't take things further but there is quite a lot you can do to hold them accountable.