was the other solution that is not satisfactory. Why not?

Because, as you've found out, repeated captures don't work. (I've often wanted it myself.)

splitting a thousand fields into an array takes about 300 times longer than selecting 3 fields out of the line

Fair enough. One alternative is to repeat the capture manually. Something like:

@jam = $ham =~ m/\t([^\t]+)\t+([^\t]+)\t+([^\t]+)/;;

print @jam;;
spam spam yam
[download]

If the number required isn't known until runtime, you can generate the regex on the fly.

Another possibility is to capture the whole lot in a single capture and then split it:

( $jam ) = $ham =~ m/^[^\t]*\t[^\t]*((?:\t[^\t]*){3})\t[^\t]*$/;;
@jam = split /\t+/, $jam;;

print @jam;;
spam yam
[download]

A real example would get answers that address the real problem.