“Leil Shishi” & Friday “To’ameha” – Do they enhance Shabbos or detract from it?

What draws men to these gatherings?
How do they impact the home — especially when alcohol is involved?
What is the halachic basis for tasting food before Shabbos?
What are the halachic concerns with entering Shabbos intoxicated or eating too close to Shabbos?
What should an ideal Erev Shabbos look like?