In Simulink, it is often the case where a user wants to connect multiple blocks to another block, particularly in case of mux, demux, and bus creator blocks. The typical practice is to select multiple blocks, hold control, and select the mux block (for example). This done, the blocks are all automatically connect. The next step is then typically a manual resize of the mux block by the user to make all of the lines just created straight.
This functional will automatically resize the block when the lines are initially drawn to eliminate the manual step of doing so.

Open the included model AutoSizeTest.mdl and follow the instructions to see an example of the functionality.