I used to keep armour unbased. However, by the time I'd put the 'Mechs on a hex base, infantry on half a hex base, done flocking etc, the armour looked a) drab and b) low.
As I happened to have hundreds of MW dials available, I ended up using them for armour bases, and works well enough for me, and makes the unit look more cohesive.
(You might get two unbased Saladins in one hex, but you're never goint to get two Ontii in a single hex. Biggest arguement for 2" hexes ;) )