Below, I have some of the best questions and answers on Bunga-Bunga Parties from the old Hotline. The answers may be out of date so feel free to correct this thread. 

What is the benefit of joining a party?  What does my admission fee buy? Conversely, what's the benefit of throwing a party? -gimpsyit

When joining a party you will get one/some random girls for your phonebook. The quality seems to depend on the price of the party. (Watch the girls participating on the provider's girls list.)

Throwing a party needs alcohol, drugs and girls. The more you invest, the more you get. You should not be greedy and bribe the local police with 95%.You can join your own party for free (same results as above). During the time your girls are not available for other jobs (massage parlour for example). You will get money, phone numbers of girls (random) and clients (random) at the brothel.

-Jack69

Does anyone know what the use is of making a party or participating in a party?  -PatPro

Making a party brings you girls, clients and money.

Depending on what kind of alcohol you use, you have more chances to get girls or clients. For example, with one beer you get 0.02 girls per hour and 0.02 clients per hour. With Leg Spreader you get 0.06 girls and 0.02 clients.The best ratio is at rum - 0.1 girls and 0.1 clients. You can see the stats after you pay the bribe, in the upper left corner. 

You can also use drugs/candy. This has no effect on girls or clients, only on the cost of the party and of course of the profit.

If you want more money, pay a small amount to the officer. If you want to play safe, I suggest paying a 95% bribe.

List with alcohol ratios:

Alcohol/Girls/Clients
Beer/0.02/0.02
Cider/0.02/0.02
Leg Spreader/0.06/0.02
Wine/0.02/0.02
Vodka/0.08/0.08
Whiskey/0.1/0.08
Champagne/0.06/0.02
Brandy/0.08/0.06
Bourbon/0.08/0.06
Gin/0.08/0.1
Rum/0.1/0.1
Tequila/0.12/0.06

-DrAg0s

I began a bunga-bunga party and I collected girls, clients and high rollers. What are high rollers? -d_ahat

[High rollers are other players who paid to join your party.]