There is an old saying that a lawyer who represents himself has a fool for a client. This maxim also holds true for an executive or manager who does not have a lawyer review their employment contract or offer letter, and negotiates the language and terms themselves.
When reading your contract or offer letter, keep in mind that employers will purposely use language that is vague to leave themselves an opportunities to exploit during difficult times. For example, sales people constantly have issues collecting commission payments upon termination because the company does not define when commissions are earned. In addition, in trader and banker agreements just because the word guarantee is used as to a bonus amount does not mean it is guaranteed if you are terminated before it is paid. These are just two examples and there are many more.
Without the experience and training of an executive attorney, there is a strong likelihood that risks you could have negotiated away will get over-looked. The time to address the risks associated with your agreement is before you execute the agreement and resign your current position. Once you are employed it is too late.
What an executive attorney can do for you is help you identify and assess the risks inherent in your agreement, and offer the best solutions for addressing the risks that are of the greatest concern. Most risks are negotiable. But, unless you know what they are and how best to address them you may experience conflict during, or upon exit from, your employment or be denied compensation you believe you had earned.