Figures are expensive, and painting time likewise.

Some armies have troops that can be represented two different ways, but the figures for both are the same.

Some examples:

• Uruk Hai Raiders in Goblin armies fight in open order.  The Uruk Hai in the more structured armies of Mordor are Elite Foot, fighting in close order. 

• Hundred Year's War English Longbowmen are on 1mu deep bases (20mm deep in 40mm base scale).  But they can have the battle card for Mounted Infantry; when on their ponies they should be represented on a square base (40mm x 40mm)

Other examples exist.

The solution is Sabot basing.  Using the Uruk Hai example above: Get a metal base the size of the Raider base (80 x 40mm).  Base the figures up on an Elite Foot base (80 x 30mm).  Put a thin sheet of magnet strip (adhesive) on the bottom of the Elite Foot base.  Then add a 3mm strip of balsa wood to the back of the Raider base and base it up nicely as well.

Result is a stand of figures that can fight as Elite Foot and (with the added sabot base) can fight as Raiders.