Substract of Dates in set analysis

[Applicable88]

Hello,

I have following set analysis:

Sum({<[Outbound.Date]={"<=$(=today())"}-{"<$(=today())"},[Place]-={'8888'},[Route]-={'T784'},[Place]={'FLZ3'},[Route]-={'WS36L'},[Status]={'V'}>}[VALUE])

I know its only works this way, but I cannot recall what implication this syntax has: [Outbound.Date]={"<=$(=today())"}-{"<$(=today())"}

What happens here with the date, when I obviously substract outbound dates which equals today or are smaller than today with dates which are smaller then today?

Does it make any sense?

Thank you in advance.

Best.