The government wants to build projects for the lease amount of money possible. Their appraisers and attorneys know this and will fight to pay you as little as possible for your property. They also know that many landowners simply take the government's offer because they are afraid of what will happen to them if they do not accept the government's offer or they believe it will be too complicated to fight for full value for their land.
Sometimes a business or property owner might be able to negotiate a fair price without legal representation. However, in most cases owners will obtain a significantly better overall result when they are represented by competent, knowledgeable counsel (i.e. more money in their pocket, even after their lawyer is paid). Eminent domain is an unusual area of the law with its own peculiar rules regarding compensation. Most owners (and most attorneys) do not know the full extent of the compensation to which landowners are entitled.
For most people, their real estate or business is their single biggest asset, and you do not want to give it away to the government for less than full value. This is a situation in which it is crucial to be properly represented by a knowledgeable eminent domain attorney.
Although you may reach a settlement prior to the government filing a condemnation lawsuit, it may be necessary to allow condemnation to occur (i.e. the government to file a lawsuit) in order for the property owner to receive just compensation. An experienced eminent domain attorney will help you consider all elements of damages and prepare your case from day one to be ready if you eventually have to go to trial. Being prepared for trial also increases the chances of settling your case for more than the government's first offer without having to go to trial and possibly without even having to go to court.