I dont know what the actual percentage loss is in skill gain by spamming the same training sessions, but if that is what you need the most, then its better than not training it at all. Personally ive never noticed much of a difference, but thats what i've read. When i have 12 straight sessions of a particular skill, given your energy and morale are adequate, the skill gain has stayed pretty high for me. If someone knows the exact percentage drop off i would love to know myself.