These are not a tree one normally associates with bonsai. But to me they are one of the most important trees I work with.
We keep a variety of sizes in various parts of the BONSAI area.
Not only do they add variety to the garden, they also offer color. We have had 2-3 plants flower in the last couple of years.
But the main reason I grow them is for water indicators. If any of these guys start to wilt from dryness it tells me the entire garden needs a drink. 
The lilac shown in the blue pots is in the 8-9 year old.
Bonsai and Burl - 