It really depends on what you are receiving and where you are receiving it from. For example, I will normally acclimate any coral if purchased from an lfs due to the extra time involved in shipping from the wholesaler and the expected poor handling from probable novice employees. Although I personally like to acclimate corals from the wholesaler, I trust them and the stock received that we've (at work) tested salinity and dropped corals directly into our holding systems after temperature acclimating. We have had success doing this with all coral varieties including Tridacna; although, soft corals, gorgonians, and clams tend to have very little recouperation time in comparison. All in all, if you want to be safe then I always recommend acclimating your livestock. I normally will temperature acclimate for 10mins. by floating a bag at the waters surface. Then opening the bag and emptying contents in a bucket, using an airline to stream water for about an hour. Every coral needs to be judged in how long it needs to be acclimated based on health appearances so 2hr acclimations are common. In emergencies, when bags come in brown, you may need to rinse the coral in saltwater or freshwater, make any fragments, and place in holding right away due to lack of proper water quality. As far as deleterious effects, most of the time if water parameters are not somewhat matching the coral may fall into a type of traumatized state internally/externally where its internal structure cannot handle the variance and begin bleaching or other maladies spring into play.