[Brightcolours]

Who defined what full frame is ?? why should 24X 36 considered as full frame  ???

Full frame just means: full 135 format frame, as opposed to APS-C and APS-H which are just partly the frame of 135 format but use the same lenses and same lens mounts. Not too hard to understand

why isn't it a crop of the 39X50.7 medium format ???

The full frame of MF is 6 x 9 cm,  4x5 is a cropped format too, like APS-C  

forget about this talk

 

As Rainer already said: if the camera does the job for you go for it 

Do you really really need shallow depth of field ? or just the opposite ? if you are shooting macro most of the time then with APS-C  you have  more depth of field you badly need, you have more distance to your subject with the same lens.

When good quality wide angles for APS-C were rare we had issues now all is solved.

If you don't feel you  need medium format then surely you don't need full frame

That is of course not true. FF gives more shallow DOF when needed than APS-C, or MFT, or compact digital cameras, or phone cameras. Sure, 6x9 gives even more shallow DOF possibilities if one has the right lens for it, and large formats even more (again: with the right lens). But FF certainly has its space, and is way more portable than large format or most MF cameras.

 

So, if one feels the need for FF for more shallow DOF, it is a smart choice. If one does not need the more shallow DOF, APS-C is fine.