Even in the absence of terrain issues, following the SID vertical profile ensures you don't stray outside controlled airspace, as the base steps up as you leave the CTR. These areas of class G can often be quite busy with light A/C etc under the TMA.
If you ever fly the MONTY/NOKIN SIDs from EGCC, (which go to 5000ft), the vertical profile ensures you stay above the NANTI departures from EGGP, which climb to 4000ft underneath the Manch' outbounds.
Last edited by ZOOKER; 21st Dec 2011 at 11:07.