I know people who do both, I don't think its any worse to take the subs twice a day but I have heard that from a lot people that are on it that the lower the dose they take the better they feel, talking about feeling normal anyways. Most of the people I know start out taking it twice a day and then after several months they only take 8mg once a day and then 4mg and so on until they are done with it.
Physically, it has no bearing. However, mentally it confirms the addictive behavior. Because of Sub's long half life, there's no reason for twice a day dosing...and, sitting there dosing to keep away withdrawals or to get a "lift" is only telling you addiction that this drug is no different from other opiates. So, that's why doctors with significant addiction experience (not just a general GP) suggest once a day dosing.