(flex.info)Why cant I use fast or full tables with interactive mode?

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Why can't I use fast or full tables with interactive mode?
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One of the assumptions flex makes is that interactive applications are
inherently slow (they're waiting on a human after all).  It has to do
with how the scanner detects that it must be finished scanning a token.
For interactive scanners, after scanning each character the current
state is looked up in a table (essentially) to see whether there's a
chance of another input character possibly extending the length of the
match.  If not, the scanner halts.  For non-interactive scanners, the
end-of-token test is much simpler, basically a compare with 0, so no
memory bus cycles.  Since the test occurs in the innermost scanning
loop, one would like to make it go as fast as possible.

   Still, it seems reasonable to allow the user to choose to trade off a
bit of performance in this area to gain the corresponding flexibility.
There might be another reason, though, why fast scanners don't support
the interactive option.