1. Kesh grow to some extent, then the energy intake by us MAY be utilized by us for other constructive purposes, which wud otherwise hv gone towards growth of hair.
2. Man with a head gear, kesh, turban looks so majestic one. Guess thats why all kings and saints or royal families used to keep those.
3. Guru ji wanted Khalsa to be identifiable always. The identity which can not hide in a crowd. One can recognize a Sikh with turban, kesh from a distance within a big crowd. Khalsa got to stand for the principles.
4. Kesh in turban acts as an air-conditioner in winter and summer, and even avoid serious brain injuries in an accident compared to helmet, due to uniform distribution of accidental impact.

Above might sound funny, illogical or whatever, but those are just my thoughts. Guide me, or point out appropriate source/link for the same to learn more about this.

With all respect to Khalsa, humbly yours, new sevadaar.