It’s never nice to practice when the conditions are bad, but this is where drivers will generally find the most amount of time.
The wet weather limits the amount of grip & traction a driver has available, so the more experienced drivers generally have an advantage having driven more laps in the process. When looking at the race track, drivers will notice a ‘shiny’ section on the track and a ‘darker’ colour surface. The shiny section is the dry racing line. But water mixed with rubber, chain lubes and grease are like ice for drivers in wet conditions.