What is the purpose of the hold at JNC on the Grand Junction Seven SID?
If you look at the chart, you'll see that after takeoff you will arrive at JNC from either the east or the northeast. Transitions then proceed back in an easterly direction (045 to 113 degrees).  With the possible exception of the Rwy 29 departure with the BRICK transition, the SID requires a course reversal at JNC. The charted hold provides a means and protected airspace for the course reversal.  

And as you surmise, some aircraft may require climbing in the hold to reach the MEA.