F=frameaccel(F,Ls);
F=frameaccel(F,Ls) precomputes certain structures that makes the basic frame operations frana and frsyn faster (like instantiating the window from a textual description). If you only need to call the routines once, calling frameaccel first will not provide any total gain, but if you are repeatedly calling these routines, for instance in an iterative algorithm, it will be a benefit.
Notice that you need to input the signal length Ls, so this routines will only be a benefit if Ls stays fixed.
If frameaccel is called twice for the same transform length, no additional computations will be done.