how bad is it to ALWAYS bet first when last to act?

[Sooga]

So I was playing on party recently, and this is something I've always noticed, but never put much thought into. There are players (many, actually), who will ALWAYS bet the flop when it's checked to them. Like not most of the time, ALWAYS. Capped preflop and a A K x flop, and it's checked to them? They'll bet it. And it's not because they have a piece of it, they bet because, I don't know, maybe they think they'll take it down there.

And that got me thinking.. how bad is this play, really? I mean obviously it's a bad play, made worse the more players are in, but if your default play is to ALWAYS bet when you're last to act and it's checked to you, exactly HOW bad is it?