That interlock is there to protect the service technician working on the machine, without it you greatly increase the risk of coming into contact with high voltage when servicing the machine. Currently you have no way to disable the high voltage for doing lamp and switch tests under the play field, some of which require you to make measurements with the low voltage circuits powered on...
Well I guess you can remove J102 from from the Power Driver board (with the power off) then raise the playfield, turn the machine back on, do your checks, turn the machine off, lower the playfield back down, reconnect J102 ... its too many steps, plus you wouldn't want to keep stressing the header pins like that.
There is a secondary danger of shorting this high voltage to a lamp or switch contact when doing checks, this would immediately blow components on your CPU and/or Power board.
Kudos to jadziedzic for suggesting the missing interlock cable; like I said earlier, I would never even considered this as a possibility. Seems like it would be more work to remove that harness than to just jumper past it.