Grantor trusts, do they ever figure into retirement plans?

[Guest Enda80]

A clarification as to what Grantor trusts are would help very much. Do grantor trusts ever figure into retirement plans?

[J Simmons]

When a grantor retains substantial control of the trust he sets up, the grantor is taxed on the trust’s income. The trust is disregarded for tax purposes.

How that figures into retirement plans? I've not run across it my ERISA experience, but if it's disregarded for tax purposes, it probably means that any significance a grantor trust has in relation to retirement plans applies to the grantor personally as the trust is not regarded as a separate tax entity.