While you have a simple question, the answer you are looking for is obviously complicated.
Speaking only for myself, a multi setup was desirable as it left more room for pins and dedicated drivers while getting the 'you should have some/more arcade machines' or 'do you have x?' people off of my back. Mame is ok if your setup is tweaked with a sweet front-end but for someone who doesn't want to go through all that and at the same time make it easy for the end user, multi seems to be the answer.
I also had a friend who I hadn't seen in years stop by last summer and check out my game room - he loved the idea but didn't think he had the time, money, or space for it. I showed him my multi setup and ended up building one for him for cost and now he is thinking about adding a pin and some other games. In this case it was sort of like crack, getting that first one in his own basement opened the door for desire for others and added another member of the community to the ranks. However, YMMV.
I know some purists scream 'Sacrilege!' from their mountain tops but for me and some others that I know, it gives some otherwise destined to be destroyed cab new life. I do understand that it is in poor taste to destroy a working classic just to throw in a multi but in the case of a game that is too expensive to fix, has parts made of unobtainium, already been molested beyond hope, etc something like this gives it new life for someone else to enjoy.