An ideal solution forms when the only driving force is the entropy of mixing. That is, there is no change in attractive forces between solvent and solute. If you will, a solvent molecule sees itself interacting with other solvent molecules and with solute molecules in the same way. Likewise, the solute molecules.

The concept of an ideal solution may seem useless, but it is a starting point for estimating many properties of real solutions in the same way that the ideal gas law helps to estimate gas properties.

In very dilute solutions, the enthalpy of mixing is small because the amount of solvent interacting with solute is small and the solute species are far apart. Entropy is much more important than enthalpy in these dilute solutions. For these dilute solutions, properties of ideal solutions are a good approximation.