1) You may be put on the localiser early (20 - 30nm away is always a possibility if airspace allows the room to manoeuver). However, descent in this case could a) lead to you infringing someone else's airspace; or b) descending in conflict with traffic possibly crossing the ILS approach at a lower level.
2) If you're being turned on so tight that you intercept the Localiser close to Glidepath intercept then ATC should foresee this happening and give you the descent clearance before intercept - "...........when established, descend with the ILS". Descending off your own back, although it might not cause problems, one day could do, so shouldn't really be done.