any point to avoiding meat and shellfish at non-kosher restaurants?

Some Jews have a practice of keeping kosher at home but eating at non-kosher restaurants, where they will be sure to avoid ordering meat or shellfish. Is there any "point" to this from a halachic standpoint? Since their food is cooked in non-kosher pots and ovens, isn't it just as non-kosher as if they would order meat? Or are they committing less transgressions (and/or less severe ones) through this practice?