First, both the EEOC and TWC begin with an investigation followed by a mediation process, where the two sides come together with a mediator and they try to reach a settlement. The employer does not have to offer you a fair deal (or any deal) and the mediator cannot advise you whether anything offered is a fair deal. The only way you will really know whether you are getting a reasonable settlement offer is to have an advocate with you who can assess the value of the offer. Additionally, many businesses will take you more seriously if you appear with counsel.
Second, and most importantly, when you file the charge or complaint, whatever you describe as the basis for your belief you were discriminated against will limit what claims you can bring to court if your charge or complaint is not resolved by the administrative process. There are many, many cases where people submitted their charge or complaint with very little details and when they received a right to sue letter – entitling them to go to court to pursue their claim – they hired a lawyer but the court would not allow the lawyer to argue additional facts or claims because none of that appeared in the original complaint or charge. To prevent that sometimes disastrous situation, you should hire a lawyer to help you draft the charge or complaint to include relevant facts to allow for a proper investigation and if necessary litigate all your claims.