A long time ago, as a man in his 20s, I was very grateful when a bus station employee unlocked the doors late at night and (after seeing that I had a genuine ticket for departure a few hours later), let me spend 3 hours indoors instead of having to stay in a rather dodgy part of a city in Latin America.
My understanding at the large London airports is that if people are genuine travellers and don't make any trouble / noise or annoy others, a blind eye is turned and they are allowed to sleep on a bench or the floor. Get drunk, are very smelly, p*ss on the floor or otherwise make a nuisance of yourself and security will throw you out pretty quickly.
It seems a shame that SEN cannot adopt a slightly more nuanced approach that involves discretion
https://www.sleepinginairports.net/l...n&terminal=SEN