Sure, it matters. The 4% interest is attractive, and it's computed monthly. Every month your dollars are earning less than 4% (when they could be earning 4%) is a clear loss.
Why not? If you're certain or near certain of the future, then you should manage your OA balance accordingly.(*) Don't forget that OA earns interest, too, so if you want $X of OA to be available on some date next year then be sure to factor in the amount of OA interest that'll be credited on December 31. (CPF interest is computed monthly based on the lowest balance for the month and credited annually. However, there's one notable exception to the lowest balance interest calculation rule: if you transfer OA dollars to SA then the transfer is effectively backdated to the beginning of the month and the interest is credited to SA at the SA rate. OA gets the lowest balance calculation.) Also, as additional OA dollars stream in from compulsory contributions, you can transfer those, too, assuming you've computed your $X OA convergence target correctly.
It's May 25 at the moment, so you have another ~5 days to run the numbers and figure out how much you'd like to transfer in order to qualify for May interest on that amount in SA.
Another possible factor to consider is that when your MediSave Account reaches the Basic Healthcare Sum and your Special Account reaches the Full Retirement Sum then the portion of your compulsory contributions earmarked for MA will spill over into your OA. If you're getting near this point then OA dollars could be streaming in faster than you otherwise might have expected. And then your OA "buffer" should increase, assuming you remain employed.
If your SA is near the Full Retirement Sum and if you'd like to make a top up for tax relief ($7,000 top up) then do that first (via PayNow QR), then an OA to SA transfer after you see your SA top up credited. If you get this order wrong then you fill up your SA to the FRS before you get your last chunk of tax relief for SA top ups.
(*) Some people -- or at least their families -- are loaded with liquid assets, and they really don't need to keep OA dollars as OA. In these happy situations the rational, sensible thing to do is to transfer all OA dollars into SA, to boost interest earning. My household happens to be in this situation.
