boot from SD or boot on BBB - flawed thinking?

I need more space than is available on the BBB. I will be using wheesy 7.2 Debian (unless there are reasons to use another linux) and have installed wheezy on the BBB and also have a boot from SD.

Should I consider just booting from the SD card and changing it to 2 partitions and extend the rootfs from the 2nd partition. Or should I boot from the BBB and just add space via the SD card.

I have seen instructions for converting a SD boot card to 2 partitions and extending the 2nd partition to be part of the rootfs. I have not seen examples of just using a bank SD card for more space.

I’m thinking if I just boot from the sd card maybe there will be some speed considerations but everything I install will be on that card right? So I can move that card to another BBB or even duplicate the SD card should I want more than one BBB to use the same software.

Help me understand how my thinking is flawed or not.