Overlap-Add versus Overlap-Save
Essentially, OS is slightly more efficient since it does not require the addition of the overlapping transients.  However, you may want to use OA if you need to reuse the FFTs with zero-padding rather than repeated samples. 

Here is a quick overview from an article I wrote a while ago


  Fast convolution refers to the blockwise use of circular convolution
  to accomplish linear convolution. Fast convolution can be accomplished
  by OA or OS methods. OS is also known as “overlap- scrap” . In OA
  filtering, each signal data block contains only as many samples as
  allows circular convolution to be equivalent to linear convolution.
  The signal data block is zero-padded prior to the FFT to prevent the
  filter impulse response from “wrapping around” the end of the
  sequence. OA filtering adds the input-on transient from one block with
  the input-off transient from the previous block. In OS filtering,
  shown in Figure 1, no zero-padding is performed on the input data,
  thus the circular convolution is not equivalent to linear convolution.
  The portions that “wrap around” are useless and discarded. To
  compensate for this, the last part of the previous input block is used
  as the beginning of the next block. OS requires no addition of
  transients, making it faster than OA.