Yankinoz, I run vacation rentals here in the Phoenix area as well. Although no guest should expect to have a garage, I do believe paying guests should have some kind of sheltered (covered) parking. Unless it's a fully-enclosed garage, it is not a security issue but a weather issue, namely the intense heat and sun here in the Valley. A car parked in direct sunlight at one's home (where it is likely to remain parked longer than any place they temporarily visit) can get to be a literal oven, with temps reaching between 150º - 200º. Not only is that very unpleasant upon entry but it takes much longer to cool down (it is can also wear on both the interior and exterior over the years, but that probably wouldn't be a concern if they're there a short period or using a rental car). That is why you will find no residence in the Phoenix area that doesn't provide some kind of shelter for the resident's vehicle, be it a garage, car port or at least covered parking. While this may not be deal breaker for all guests and some may not even complain, it is a definite detriment or "con" for people who may want to rent your place if they should ask in advance (and even if they don't, they may express displeasure upon arrival). Whatever you decide, consider those things.
By the way, the high in Phoenix today: 113º (and summer doesn't even start until Wednesday!)