Professional Development budgets can be hard to spend. Spluring everything on a conference gets you some half-decent benefits - something to put on your self-assessment for your review cycle; a couple of days out-of-the-office; some half-decent food, snacks, and corporate gifts; and finally the chance to travel to an interesting new city on your company's money.
How you put going to a conference on your self assessment?
> Personal improvements this year
> Went to a conference, learned a bunch of stuff on company time
> Business value added this year
> Went to a conference and got better!
Or what?
Usually "increasing your skills and knowledge" is not part of performance reviews. They are about your work performance (Duh). I.e. results, not learnings.
Professional development plans and activities are often a line item.