  Image diffusion models have been utilized in various tasks, such as
text-to-image generation and controllable image synthesis. Recent research has
introduced tuning methods that make subtle adjustments to the original models,
yielding promising results in specific adaptations of foundational generative
diffusion models. Rather than modifying the main backbone of the diffusion
model, we delve into the role of skip connection in U-Net and reveal that
hierarchical features aggregating long-distance information across encoder and
decoder make a significant impact on the content and quality of image
generation. Based on the observation, we propose an efficient generative tuning
framework, dubbed SCEdit, which integrates and edits Skip Connection using a
lightweight tuning module named SC-Tuner. Furthermore, the proposed framework
allows for straightforward extension to controllable image synthesis by
injecting different conditions with Controllable SC-Tuner, simplifying and
unifying the network design for multi-condition inputs. Our SCEdit
substantially reduces training parameters, memory usage, and computational
expense due to its lightweight tuners, with backward propagation only passing
to the decoder blocks. Extensive experiments conducted on text-to-image
generation and controllable image synthesis tasks demonstrate the superiority
of our method in terms of efficiency and performance. Project page:
\url{https://scedit.github.io/}
