In free-radical cross-linking (co)polymerization of common multivinyl monomers it has been conceived that the greatly delayed gelation from theory is due to microgel formation. This was discussed by pursuing the gelation in free-radical cross-linking polymerization of diallyl terephthalate (DAT) in the coexistence of a preceded cross-linking polymerization of ethylene glycol dimethacrylate accompanied by in situ methacrylate network-polymer-precursor (NPP) formation since in DAT polymerization the primary-polymer-chain forming reaction could be controlled by the allylic hydrogen abstraction of growing polymer radical from allyl monomer, and thus, any gel effect inducing the complication of the polymerization system is not observed at all. Thus, the preceded in situ methacrylate NPP formation promoted the gelation, never leading to delayed gelation. The role of high-molecular-weight NPPs ranging from an ideal NPP to a nanogel-like NPP on the gelation in DAT polymerization was then pursued by SEC-MALLS-viscometry; the addition of high-molecular-weight NPPs clearly promoted the gelation, and strikingly, the role of nanogel-like NPP was never as an inactive polymer particle leading to a delayed gelation.