Military Branches have ranks from E1 to E9 and then officer ranks from O1 to O11. In Battletech, Rank determines your skill as a pilot and a leader, with heavier chassis being available the higher rank you hold.
in short, your rank should determine what weight chassis you can hold.
Say for instance You have a drop weight of 320 tons with 3 Stalker and a Locust for S&Gs and a pilot pool of an O5 an E9 an E5 and a
in a game without ranks we would most likely see that E1 in an Stalker forcing other players to conform to a now diminished team due to weight limits.
in a game with earned ranks, that O5 (which for the sake of gaming is an E9 + 5) and that E9 can jump for those Stalkers leaving the E5 and E1 to fall in their respective places. the O5 can vouch for lance (4/4) and maybe even team (4/8/12/16) command if he's ranked high enough, OR he can pass is down to the E9 who needs a bit more practice.
TO CONCLUDE: by adding a mechanic to weight limits in which players with higher skill (given by rank and some other math) are given weight priority over those who are less experienced can increase the value of heavier chassis AND light mechs, while giving those who are less prestigious something to work for, on top of mech experience.