Answer: Most lilacs mature to a large size, almost like a small tree. They can be pruned smaller but regrow to regain their size quickly due to their established root system. Also, the only time to prune without sacrificing flowers is right after their blooming period in late spring. (Pruning at other times will remove flowering wood.) If you have a lilac that is way too large it might be better to replace it with a smaller maturing plant instead, perhaps a dwarf lilac or something else entirely.
Q&A Library Searching Tips