The key point here is repeatability: come back to the very same place year after year (in the spring after fall, etc.....)

As all GPS related signals, RTK, but as well all other signals (Omnistar, SF1, SF2, Beacon, WAAS) rely on primary signals from GPS satelites. Therefore, when there is a bad constellation (not enough satelites, all satelites at the same angle) GPS signal is too bad to be used and all those positionning systems have problems. With any correction other than RTK, you have to do some manual adjustment to your position over time.

You mentionned planting after having fertilized..... When using anhydrous amonium, you have to be carefull not to plant where NH3 has been applied or wait for at least a week because of seed burn. With RTK's repeatability, you can come right after NH3 application and be sure you will be off the fertilizer row if you apply an offset.

My 0.02€