When I used to have a lot more disposable income I used to do this kind of thing all the time. If I would go out to eat with friends, I would very frequently make a habit of paying for everything.
I'm not sure why I did it, honestly. I think I just wanted to do something nice. I also figured it would just be a nice gesture to "take care of the bill" so that everyone else wouldn't have to worry about it and could maybe relax and enjoy the rest of their evening without the possibility of them being concerned about how much money they had spent. I think on some level I felt guilty about other people spending money. And when I would buy someone a meal or buy them a few drinks I wouldn't want or expect anything out of it. To be honest, it made me a little uncomfortable if people made a big deal about it or even said anything more than "Thanks".
I've had times in my life when I've had extra money to spend and had times when money has been tight. And I know I've experienced occasions where money is tight and you go out for a meal with friends and spend a portion of the night feeling guilty that you're spending money. I think that when I had extra money, I just wanted to make sure that no one was feeling that way. I just wanted to give them the opportunity to enjoy the night, or enjoy lunch, or whatever it was we were doing.
I generally don't pick up the tab when going as a group. For one thing it gets expensive really fast, and secondly you just don't get the same "mileage" from it.
The amount of good will you receive when paying for a 1v1 meal is a lot greater than the good will you receive when paying for the whole table. It's the personal touch I suppose, the feeling that you did it for him/her, as opposed to "them".
This goes back to the issue of, 'Why are you doing it?'.
In my situation I wasn't doing it to receive any "amount of good". I was just doing it to do my friends a small gesture. And if I could do 5 friends a small gesture, that's probably more gratifying to me than doing only 1 of my friends a small gesture.
I (an Intl. student) usually try to buy meals of my friends (mostly Americans i.e.) but hardly get anything in return (I really don't expect anything in return any way) i.e. they act cheaply sometimes even though they have the $$ and live affluently - this is the trend I've noticed since my undergrad years (some of my other Intl. friends have echoed similarly) Yes, I was born in a different culture, where guests mean a lot to us, but it's more than that - a sense of gesture and common-sense (may be?).
If you're oriental you're in for a shock. Westerns tend to be a little, ummm, cheap. Gifts are not valued by them as they're in the east. OTOH, some orientals, specially arabs and chinese will probably bankrupt themselves hosting lavish dinners for others; while not a good idea, it at least buys them some social capital. Whoever takes care of the others is taken care of by all. While to Westerners, if you're out of money you have no recourse but the bank.
I'm not sure why I did it, honestly. I think I just wanted to do something nice. I also figured it would just be a nice gesture to "take care of the bill" so that everyone else wouldn't have to worry about it and could maybe relax and enjoy the rest of their evening without the possibility of them being concerned about how much money they had spent. I think on some level I felt guilty about other people spending money. And when I would buy someone a meal or buy them a few drinks I wouldn't want or expect anything out of it. To be honest, it made me a little uncomfortable if people made a big deal about it or even said anything more than "Thanks".
I've had times in my life when I've had extra money to spend and had times when money has been tight. And I know I've experienced occasions where money is tight and you go out for a meal with friends and spend a portion of the night feeling guilty that you're spending money. I think that when I had extra money, I just wanted to make sure that no one was feeling that way. I just wanted to give them the opportunity to enjoy the night, or enjoy lunch, or whatever it was we were doing.