[pradn]

SWE-years are actually used for two things: a) measuring ongoing cost and b) for calculating if an investment will pay off.

There's a few benefits over just using a dollar figure. It's a unit that natural ties time to value. SWE-years is a natural unit for thinking about the time of SWEs. It's also convertible to other units. The conversion factors to other units can change over time, without having to pay attention to the minutiae.

All these factors make it useful for both measuring ongoing cost and making investment tradeoffs.