I still remember playing MW4:mercs and going solo with a Flea armed with only an auto cannon for as long as possible. Really helped fill the bank account early on.
I don't play MWO though, so I'm not sure how it could ever be useful there?
I remember that in MW4Mercs, being sponsored by Wolf's Dragoons gave you bunch of Fleas. Selling those filled bank account early on :P
In MWO it will be mostly a "joke" machine, i think, something you'll take to have some fun. Small size and MASC mean it will be difficult to hit so in theory a skilled pilot can dance around enemies and slowly wear them down. In practice, the 'Mech will keel over the moment someone looks at it angrily, just like the Locust.
EDIT I guess it makes for a fine scout in large games due to its extreme speed, but i don't play those.
Still remember when a brave Locust pilot took on my Atlas. Locust center torso, meet AC/20; AC/20, meet Locust center torso...