Can't promise I'll never toe the legal line but I won't try to use my birthday as excuse.
Yeah, basically people will cut you more slack and be less quick to judge you because they don't want to ruin your special day. It's like a sacred thing. A day where self-indulgence isn't a sin and you get tons of free shit. People go out of their way to make you happy and don't expect anything in return.
The only downside is if you're weird about getting old or being the center of attention.