Like many potentially performance enhancing strategies, heat acclimatisation is all about being intelligent and knowledable regarding what you are doing and what you want to achieve from it. If your goal is to improve performance in the heat, there is no doubt that a properly done heat acclimatisation intervention IS beneficial. If your goal is to improve performance in thermoneutral conditions, there are a number of physiological adaptations such as increased plasma volume and an increase in heat shock proteins, that may lead to enhanced performance. But as others have already noted here, if you over do it, then you simply increase the overall stress on the body which can lead to maladaptation instead of a positive response.
For the record, without wanting to come across as a big headed know-it-all or anything, I do actually have a PhD in exercise physiology and many yrs experience working with elite athletes