Take SSE2 instructions as an example (Every X64 processor supports these, the old x87 FPU has been obsolete for over 10 years). You can either calculate 4 floats per instruction or 2 doubles per instruction. Similar considerations also apply to ARM.
Also even if you might want to use doubles as intermediate representation you still might wish to use floats as storage. E.g read from float, convert into double, calculate stuff, write back a float.
Take SSE2 instructions as an example (Every X64 processor supports these, the old x87 FPU has been obsolete for over 10 years). You can either calculate 4 floats per instruction or 2 doubles per instruction. Similar considerations also apply to ARM.
Also even if you might want to use doubles as intermediate representation you still might wish to use floats as storage. E.g read from float, convert into double, calculate stuff, write back a float.