Hello, as far as I understand, mchip is just another more detailed measurement for EV. MonkerSolver as an example outputs the EV of certain plays in mchip.
The conversion is the following (from Episode 9: Opening Ranges in Early Position):
1000 mchip = 1 Small Blind -----> 1 mchip = 0.001 Small Blind
2000 mchip = 1 Big Blind -----> 1 mchip = 0.0005 Big Blind

As you see, the relation between mchip and Small Blind is the same as millimeter and meter. This probably makes it easier to describe the EV of marginal plays, for example opening raising hands in EP that are the bottom of our EP RFI range.
For example the EV of opening KK66r in EP is 31 mchip (MonkerSolver solution in Episode 9 at 28:44). If we would want to use BB to describe the EV of opening this hand, we would convert it to 0.0155 BB (31 * 0.0005 BB).
At least from my point of view, 31 mchip is a much more user friendly measurement instead of 0.0155 BB, similar to using millimeter instead of meter when you are dealing with smaller dimensions.

Hope that helps.