Symbolic names of global declared variables can be used in assembler routines because proper variable address will be assigned to those names by EQU directive:
Dim varname As Byte
varname = 0
ASM: MOVLW 0xFF
ASM: MOVWF VARNAME
When working with inline assembler code, it could be useful to use working register as a source or destination in assign statements. For that purpose WREG keyword should be used and the compiler will take care of the bank control:
Dim varname As Byte
ASM: MOVLW 0xFF
varname = WREG