Bad monitoring is the no.1 cause of mixing problems given some ability, if you cannot be sure of what you are hearing you have no chance of getting a good mix together. It is quite basic and yet overlooked. Once people have monitors they must be able to make great mixes right ? Well not necessarily, huge differences between monitors even though they are supposed to be flat, couple that with the ambiguity of being in an untreated room and it's easy to get it wrong. Getting the speakers and the right acoustic treatment means so many barriers between you and a good mix simply vanish.
Yeah totally! Ive found that luckily i used to mix on my monitors so I have a really good perception on what mastered tracks sound like thru them but yeh buying from new with no references could be damaging! I always reference on headphones and lappy speakers regularly thru a track to make sure stuff is hitting right, can show things up about lack of room treatment immeadiately - especially as i dont have any atm :/