An idealist is defined as a person who is guided more in life by ideals than practical considerations. A realist is defined as a person who accepts a situation as it is and is prepared to deal with it accordingly. I do not think anyone is a purist in either of these. Meaning that we all exhibit characteristics of each depending on the circumstances we find ourselves in. I do believe however, that we tend to lean more strongly in one direction than the other. This can be influenced by upbringing, life experience, education, vocation, and so on.
The idealist is good to have in the room because they push us toward a desired outcome. If the outcome they are pushing toward is right and true, it can be very helpful. The realist is good to have in the room because they see the situation not just as it could be, but as it actually is. They deal with the facts at hand and determine how to proceed based on the reality of the moment.
The idealist can easily get bogged down and frustrated if things are not moving quickly enough in the direction they think it should be going. The realist can sometimes become negative they are good at identifying problems, but may not be as adept at suggesting solutions.
What is a good approach in dealing with both from a leadership perspective? Encourage the idealist, and listen carefully to what they have to say. Their creativity and vision for the future can be an asset to a team or organization. Take heed to what the realist has to say, because they can help you identify problem and avoid pitfalls.
Ultimately it is a blessing how God wires people with different personalities and abilities. Do not be afraid of differences among your team or in your church, because this can ultimately be a blessing. The variety of personalities, brings strength and a broader perspective.