The two aren't really all that similar. Trading is just a small (albeit critical) part of the fund business. If you WANT to get into the fund business, then seeding with your own assets is certainly a great way to make that happen.
Say hypothetically you are successfully trading your own assets... What are the considerations versus starting a fund?
On the plus side, the most obvious one... you make more money. More gains when your strategy is up, same amount of losses when you are down. You also get to share your fixed expenses, be it Bloomberg or data feed.
On the down side, you have all of the typical overhead of a business. More filings, registration tests, registration fees. You need business card and letterhead. You need a phone line and a web presence. You might need to manage employees (both due to increased trading AUM and to "prove" you have operational capability). You have SEC / NFA regulatory hurdles, as well as state by state filings. You have to pay for an audit / generate tax filings. You have to market your business, and then follow up on leads... And you have to do this for years without any real money coming in. And when investor capital comes in, it's not any easier. Now, you'll get calls about your portfolio weight... Are you in cash right now? Why the hell not? Why are you down so much this month?
So, again, trading success is just a small part of deciding whether this is a good path for you. Personally, I enjoy starting up businesses, and I had a lot of capital to work with... So I didn't mind the initial overhead when all I'm doing is writing "pointless" checks. The first few years I was 95%, then 85%... Then 75% of the fund. Finally this year (start of my 4th) I'm on the verge of falling below 50% of AUM, which means the business is really finally "a business". But it's been a long trek and I'm definitely not sold on the long term value or viability.