I repack archival tapes at three month intervals and new tapes before use. Until now I've had one dropout in about 25 recorded hours (dropout replays from tape every time as opposed to capture glitches), but this does not mean that repacking is responsible for my low(as compared to reports in other posts here) dropout rate. Thin films, like video tape, can stick to itself under certain conditions. Repacking can reduce the chance of problems from this when recording or capturing.
Repacking is recommended by the manufacturer. It seems harmless and may be helpful, that is why I do it.
Use of a cleaning tape is also recommended, but I don't follow all recommendations
If you're repacking it makes sense to buy a rewinder for the job to limit wear and tear on the cam. Some rewinders only rewind and some FF also. Obviously one that does both FF and RW is better.