Something many people do not understand- and which can harm them in their case- is that as soon as you are on notice of litigation or potential litigation you are under a legal duty to preserve evidence. Negligent or intentional loss or destruction of relevant evidence is taken very seriously by the courts, and can result in severe sanctions, including dismissal or default.
You should also know that in today's technology environment, it is usually virtually impossible to completely erase information that once existed.
It is also important to recognize that your own attorney needs to know everything- the good, the bad and the ugly. If you lose or destroy information that is in any way part of the case, you may be interfering with your attorney's ability to organize and present the evidence in the way most favorable to your case.
Learn more here about discovery in a civil lawsuit.