Depends on the situation, for left aligned numbers it didn't matter because
you can't see where the space comes from (1) but for right aligned numbers
you need a postive value for distance (2).

(1) Left aligned number:

\starttext
\bTABLE[frame=off]
\bTR\bTD[width=1cm] 1 \eTD\bTD header \eTD\eTR
\eTABLE
\bTABLE[frame=off,distance=5mm]
\bTR\bTD[width=5mm] 1 \eTD\bTD header \eTD\eTR
\eTABLE
\stoptext

(2) Right aligned number:

\starttext
\bTABLE[frame=off]
\bTR\bTD[width=1cm,align=flushright] 1 \eTD\bTD header \eTD\eTR
\eTABLE
\bTABLE[frame=off,distance=5mm]
\bTR\bTD[width=5mm,align=flushright] 1 \eTD\bTD header \eTD\eTR
\eTABLE
\stoptext

> Hans wrote:
>>> - maxwidth ?
>>
>>just try it on long entries .. it prevents too long lines
>>
>>this is a very long entry
>>this is a very ...
>
> Ok I see. Now, in \placecontent or \setuplist, which parameter
> allows to influence where long lines are cut off in two (or more) ?
>
> Like...
>
> (number) This long long
> chapter title                       (pagenumber)
>
> vs.
>
> (number) This long
> long chapter title                (pagenumber)
>
> Using the brute force tactic I tried setting width and textwith which didn't
> work.
> It could be textcommand. If so what does \command#1 mean ( see main
> manual pg 150 ) ?

The effect for maxwidth (3cm in my example) is this:

\starttext
\limitatetext {This long long chapter title} {3cm} {\unknown}
\stoptext

Wolfgang