We do recommended that you rehydrate your dried yeast. Proper hydration helps ensure a healthy fermentation and is especially recommended for beverages with a starting gravity above 15 plato (1.061 starting gravity). Not hydrating yeast could cause a longer lag time until your fermentation takes off.
Beer
Most dried beer yeasts (Cellar Science, Fermentis, Lallemand) will tell you not to rehydrate and to pitch directly into the fermentation. They include "extra" cells of yeast to account for an amount of attrition and cell loss when pitching directly. Rehydrating the yeast prior to adding them to wort will help acclimate them and take on some water to repair their cell walls from the freeze-drying process. This will cause more cells to survive the transition from dried form to actively fermenting.
While rehydrating you can use nutrients if you like to. If you have a particularly high gravity or low target temperature the impact of the nutrient will be more noticeable.
Wine
For wine yeast we recommend that you always rehydrate your dried yeast with specific rehydration nutrients. Since you only have fruit and make wine once a year, you have a lot riding on the yeast starting fast and strong. The rehydration step with FermStart or GoFerm will make sure the yeast are healthy and ready for success in your wine fermentation. Yeast nutrients are important especially if your wine is high in acidity or starting sugar (over 25 brix).
There is no real drawback to rehydrating your yeast. The time and effort it takes to rehydrate will have a great return when your yeast ferment faster and stronger and produce a better finished product. Yeast health is super important as yeast are the most important variable in all of fermentation.