The panelization depends on size of board, how it is going to be assembled and broken, what components are there etc. In PCB house, they do not really care if it is one board, three different boards or four same boards.
Also, in PCB house they many times will put your board into much bigger panel with other boards where they often also add a lot of additional stuff on the PCB (e.g. special things where they measure thickness of each layer, where they check if PCB is ok, where they can measure impedance, etc).
However, assembly house does care about your panel - for example they require some strips to be able to transfer or fix your PCB in machine ... and also they need to have it designed the way, that components what are hanging over board edge are not going to be in way of board separation or board soldering (e.g if you use V-cut, you should not have there component in a way where boards are going to be separated).
So, if you would like to be sure about recommended size of panel, strips width or other requirements (e.g fiducials placement, additional mounting holes) you can ask at your assembly house. Or have a look at some of our open source projects (for example http://www.imx6rex.com/application/i...lopment-board/
) that could give you some ideas (I do not remember the exact measurements, I usually use similar stuff from previous projects .. and the size of panel or strips is also a little bit different between projects)