Downside of deploying a DLL that is part of GAC, on the bin folder?

Downside of deploying a DLL that is part of GAC, on the bin folder?

Is there any downside other than the increased package size, for deploying
a DLL that is part of the GAC?
What should we be worried when we do this? I believe GAC DLLs win over
local DLL, so worst case scenario, if the target machine does not have the
DLL on GAC and the local DLL is for 64 bit but the target machine is 32
bit, I can see a problem. But in this case, deploying the DLL as local
copy does not make it worse.
I am not suggesting to put everything on local copy. I am wondering if
local copy approach is to be considered as "safer way".