you don't NEED a tweecer, but ...
you are still "fooling" the computer by letting in more air than the computer thinks is coming in. the extra air is compensated for by the injectors, so it should run fine.
most of the decisions the computer makes are dependent on the perceived load. it uses the amount of air reported by the maf to determine the load.
in your case, the actual load will be higher than the load the computer calculates, so its decisions (like spark advance and target a/f ratio) will be less accurate. specifically, a/f could be targeted too low and spark may be advanced too far (because the computer thinks there is less load then there really is). this could result in detonation.
that said, the difference in load is probably not enough to cause real problems, epsecially if you have an afpr. then if you do get detonation in the higher load ranges, you can up the pressure to get around it (but then you are probably too rich down low).