It prevents you from fully interacting with the people who are actually around you when you pull out your phone every 30 seconds to fire off a quick text reply.
There is absolutely no reason to check your texts on a continuous basis, as they come in. It makes you nervous and instills a perpetual low-grade anxiety in you.
If it's an emergency, they'll call you. If it's not, then it can wait.
tl;dr check notifications in batches, at predetermined checkin points, rather than continuously throughout the day. You'll be happier for it.