Question regarding register renaming in modern processors

[rahdirs]

I was reading a paper from MICRO which says the following :

Register renaming was first proposed by Tomasulo in his well-known scheme for out-of order execution for the floating point unit of the IBM 360/91 in the 60s. In that scheme, destination operands were renamed using the identifier of the reservation station that would produce them. This scheme is not used by current microprocessors, since it requires that the reservation station be occupied by an instruction until its execution completes. Current microprocessors release the issue queue entries (reservation stations in Tomasulo’s nomenclature) right after being issued, which is more effective in terms of efficiency

I understand the part where he says that TOMASULO is inefficient as it uses reservation station's ID till the instruction commits. But, i don't understand the statement

Current microprocessors release the issue queue entries (reservation stations in Tomasulo’s nomenclature) right after being issued, which is more effective in terms of efficiency