If you do not respect your notice period, the employer has the overhand. EMployers can then do as they please as you are the one breaking the contract - you may loose monay and reputation at that game. It all depends on your present employer and how well you come along together. You are the vulnarable one in that case.
Therefore the experiences will differ considerably and will not necessarily relate to your present experience. You have to know your employer or get to know him on that point in a serious meeting. The risk of a legal case seems low because this is more costly than just letting you go. But the little anoying thing they can do to get back at you may be very irritating and cost you some monay. You know if it's worth it.