I've had a 6" for 30 years....
I still have one, but on certain projects you need a wider surface flattened. Boards come rough saw in common widths of 6", 8" and sometimes wider. A jointer is needed to flatten rough sawn or twisted boards before planing. For edge jointing only, you don't need a 8" wide jointer.
So, depending on your source of wood, rough sawn or pre-surfaced, your choice of jointer will make a difference in how you prepare the wood.
There are ways to flatten a wide board in a planner using a sled. There are ways to edge joint a board using a table saw and a sled. I have used both with good success.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)