If you are going on holiday and will not be taking your car, then this may be the perfect opportunity to get the work done at the car garage. It may be that they have previously told you that they will need the vehicle for a few days to fix a fault but you simply have not had a convenient time where you can be without your vehicle. If this is the case then call the garage and discuss it with them. They may be happy to do the work when you are away but if the job is only going to take a day or two and you are going to be away for a week or more, they may need the space so will probably want someone else to come and collect it. IF you leave it with them and don’t prearrange it, you may find that you are lumbered with storage fees.
It is always a good idea to have someone they can speak to about any repair work in your absence. Especially if you are going abroad and they may not be able to get in touch with you. As if they find something else that needs prior authority to repair, they need to have someone they can obtain the consent from.