You're doing very well as a self-employed CPA and have some great clients. To encourage them to stay that way, you decide to spring for a weekend getaway to a very nice (expensive) golf resort on a beautiful lake for around 10 of your "besties" (clients) where you'll have half-day presentations on current tax topics by guest speakers on both Saturday and Sunday, then everyone goes and golfs or whatever.

You didn't become successful by not being smart, so you know that your clients will be reluctant to attend, and in fact probably won't attend, unless they can bring their spouses or "plus ones." So you invite them, too.

The question is: will you also deduct the costs allocable to these guests on your Schedule C? Why or why not?

This is not a question about what kinds of expenses are deductible generally - there are certain limitations that would apply here. The only issue you should focus on is the deductibility (or not) of the expenses that otherwise yes would be deductible but are attributable to the spouses and other "plus ones" rather than the clients themselves.