It's normally 'Less haste, more speed'. It means that if you don't rush a task, you will actually achieve it faster, since you won't keep mucking it up as you hurry!
It means that if you try to do something too fast, it often goes wrong and/or you have to do it again, so you spend more time on it than if you'd tackled it a little slower the first time. The problem is that very often you don't realise you're doing something too fast until it does go wrong, at which point it's too late!
The phrase is based on the Latin adage 'festina lente', meaning literally 'hasten slowly'. In other words, if you have to hurry, do so with care. It is the motto of the Onslow family...'on-slow', you see!
I read the http://www.dictionary.com/
definition of haste which implies an 'overeagerness to act'. However the Oxford dictionary states that haste simply means 'excessive speed or urgency of action' which seems to make the phrase make more sense.
"Wisely and slow; they stumble that run fast."
William Shakespeare