Depends on what you mean by merge for normal/home use.
Let me give you an example. Assume you have 2X256kbps(32KB/s) connections.
Now if you want to use both at same time, you CANNOT get 64 KB/s from this connection.
However, you do get more bandwidth in the sense that if you could run 1 download earlier at 32KB/s, you should be able to run 2 downloads now. Kind of like parallel processing.
Thats my understanding at least.