Age-. The general rule in the industry is that once an A/C unit reaches 10-15 years, the idea of replacing the unit is usually a much better investment than putting money into an older system. If your system is at this threshold, it's usually wise to begin expecting, not wondering, when the system will fail.
You can keep the money in the TSP after you leave your federal job to benefit from the low fees, or you can roll over the money into an IRA or a new employer's 401(k), 403(b) or 457.
Once you leave an employer, you have the right to rollover your 401k's, 401b's, 457's, or TSP. Remember, this rollover can be done with most retirement plans including pensions and TSP (Thrift Savings Plan).