Planes are very useful when making small adjustments to timber. For instance I often use mine for planing edges from doors that don't fit properly.
You can buy a traditional hand plane but I now always use an electric one which you can now buy for as little as £25 for a DIY one (or hire one for even less). They are very effective. They have an adjusting knob which you turn to plane more or less off.
Be careful planing wood with an electric planer they can be dangerous if not treated carefully. The powerful cutter spins at very high speed and can cause injury.