I don’t think of personal finance has budgeting. I think of it as related to investment. When you say “personal finance planning” I think it means planning your personal finance future and only good can come out of planning your financial future. I don’t think “personal” finance planning means that you do it all by yourself. You would use outside resources (advisors. tax experts, etc) to help determine what you should do.
There is a con of doing it all yourself = you can’t be an expert in everything (knowing what options are available, knowing the tax consequences, etc) so if you do it solo you might not be able to collect all the best information.
There are some cons of financial planning. You should know that financial planning cannot add your money but they just manage your money. Read book, journal, magazine, and blog. Read also my blog
I’m not sure what you mean by personal financial planning. Where you yourself sit down and write a budget, financial goals and so forth? I doubt that is what you mean because there are no cons to that. If you are talking about hiring a personal financial planner, there are plenty of cons: (1) they take a fee for their service which reduces your rate of return, (2) they often are paid commissions on the funds they put you in, which means they are anything but impartial, (3) most financial planners claim they are treating you according to your specific needs, but actually are just using a simple and well-known formula to split your assets based on your age, (4) there are many planners that are competent but also many that are very incompetent, (5) they don’t respond to market changes as quickly as you would if you handled your own money. So when the market dropped in 2008-2009 many people trusted their planners to get them out and instead lost a lot of money.