Do you remember the three-martini lunch?  Probably not.  It was popular in the Mad Men era when people regularly drank alcohol at lunch, but changes to the tax law decreased the deductibility of business entertaining over time. The major benefit of business entertaining is now the strengthening of personal bonds that can lead to more business.

You may have an expense account or entertainment budget at work, but even if you don't, it makes sense to spend some of your own money on business entertaining.  You are investing in your business in a similar way you would buy a newer laptop computer or better smartphone. Here are 10 reasons why it's still a good business strategy:

1. You get to know each other on a personal level. When a relationship is "business only" it often becomes transactional.  Clients are looking for the lowest price, so they will stay with you until someone gives them a better deal.   When you get to know each other as people, you decide if you like that person.  Bonds are strengthened.
2. Your phone call gets through more often. People who know each other on a personal level tend to enjoy learning about each other's lives.  These conversations give them pleasure or keep them entertained.  They will take your call because they want to hear what you have to say.
3. Everyone eats lunch. You know how difficult it can be to get an appointment for a business meeting.  This is tougher when a few people need to be assembled.  Offering to buy lunch, whether in the office or out in a restaurant, comes across as a good use of time.  They were intending to eat.  You want to meet.  Let's get both done at the same time.
4. Drinks or lunch are a lever for introductions. You want to meet someone.  They don't know you, but they know a friend of yours well.  Your friend is willing to provide an introduction, but they don't know how to bring it up in conversation.  You suggest lunch.  You will be buying.
5. People like things that are free. You have heard the expression "There is no such thing as a free lunch."   Some people still don't believe that, or more accurately, they are willing to trade some of their time for a free meal while they listen to a sales presentation.  Mutual fund and annuity wholesalers have been doing this for decades.
6. Lunch is a good way to thank someone. They championed your case to the next level of management.  You made the cut and can present in the next round.  You want to thank your client, yet realize the rules are very strict about gift giving.  Ask your compliance people if taking someone to lunch as a thank you is acceptable.
7. You learn what's going on behind the scenes. Your client's company might have been acquired.  Maybe there is a reorganization taking place.  You want to know who is likely to be where during this game of musical chairs once the music stops.  Your friendly client might not tell you on their office phone, but they would speak plainly over lunch.
8. You can get onto someone's radar. There is an entire category of restaurants people would love to try but would not spend their own money because they are too expensive.  They are called expense account restaurants for a reason.  When you call and suggest meeting over lunch, you can suggest that restaurant as an incentive to accept your invitation.
9. Friends don't fire friends. If you have lunch regularly, you often become friends in addition to business colleagues.   If you client's firm is thinking of changing vendors, your friend might fight in your corner.  They might signal who you need to cultivate at the firm. Friends want to help friends

10. Lunch is a good place for roadmaps. You want to take your business with the firm to the next level.  You have certain product areas in mind.  You do not know who to approach at that firm.   Taking your friend at the firm to lunch and explaining what you have in mind gives them the opportunity to tell you what you should do next. 

Having lunch with people you like is enjoyable.  It can also lead to business.  It's been that way for decades and is unlikely to change soon.