Yanking an orchid out of its pot, cutting away old roots and putting it in a new container is a traumatic experience for the orchid. Orchids are pretty sturdy though, they usually bounce back in a short time. There are a few things you can do to speed their recovery. In years past it was conventional wisdom to keep newly repotted orchids dry until growth was well underway. This was based on the premise applied to other plants; roots would grow to seek moisture if none was readily available. Now, it seems many growers prefer to water them normally. The remaining roots are alive and in good shape (otherwise they would have been removed) and the fresh medium is well aerated. The additional humidity provided by the medium of a normally watered plant provides a humid environment less likely to desiccate the orchid. It is a good idea to water the media rather that the plant. Weak plants are more susceptible to fungal and bacterial infections than healthy, established orchids. Many growers actually put inactive divisions into empty clay pots that are watered normally. The surrounding high humidity provided by the damp pot can often carry the plant until new growth begins, then it can be potted normally. This technique works especially well with back bulbs.