In my collection I have this little leaf lilac bonsai (Syringa microphylla). This tree was found on a local biowaste disposal unit, and when I got it, it was little more than a little stump. It has taken a few years to get some branches on it, but 3 years ago I for the first time had a decent show of flowers.
Fast-forward and I have developed a bonsai with a pleasing canopy and loads of flower buds. With lilac however, the flowers grow in clusters. If you just let them grow freely, they will overwhelm the tree and all you see is flowers. Therefor I do a few things. I wire the tree in fall, and prune back branches without flower buds. In spring, I wait until the flower buds are well developed, and I prune these back, and remove most of the spring growth. This way, the flowers are more reduced in presence, yet stand out.
Lilac bonsai canopy structure 
Lilac bonsai budding out
A few benefits for the tree are of course an increased amount of light in the canopy, which stimulates back budding. The pruning of the growing tips does the same thing. And finally, removing part of the flowers reduces the energy the plant spends on flowering, and you get better growth in the season following.
I have captured the spring cleanup process in a short video. Enjoy!
