I hope it's not bad form to link to other sites, but I wrote some on this topic here on this post, in a thread with a lot of other good insights on this question:
http://www.bogleheads.org/forum/viewtopic.php?f=1&t=111620#p1622457Also see this post for more links on this theme:
http://www.bogleheads.org/forum/viewtopic.php?f=1&t=111399#p1619660Short answer:
There are very good reasons to transfer some of your assets into the TSP, in particular the G Fund and the low expense ratios,
but you might want to consider keeping some money outside the TSP so you can do the following:
- Hold money in certain asset classes in your favorite flavors that are not in the TSP.
- If you retire early, and find yourself in a low income tax bracket, then you might want to keep some Traditional IRA money outside the TSP you can do Roth conversions while paying little or no income taxes on the conversion. You cannot currently do Roth conversions inside the TSP, although this could change in the future and the TSP is evaluating that change.
- But even if in the future you can do Roth conversions inside the TSP, the TSP withdrawal rules currently require you to withdraw money proportionally from Roth and Traditional (e.g. if you have 75% of your account in Traditional and 25% in Roth, then when you begin RMD, the RMD must come out 75% Traditional and 25% Roth), which might not be what you prefer. You'll have more varied withdrawal options outside the TSP, enabling you to withdraw strategically so as to minimize taxes. Again, these rules could change in the future.
Bottom line, as much as I like the TSP, there are some good reasons to keep some money outside.
Note that if you are in backdoor Roth IRA territory, and to make backdoor contributions advantageous, then your only option might be to NOT hold any money in traditional IRAs. In that case, you should transfer your traditional IRA into a 401(k) or the TSP so that you can make backdoor Roth IRA contributions.